System and method for network vulnerability detection and reporting

ABSTRACT

A system and method provide comprehensive and highly automated testing of vulnerabilities to intrusion on a target network, including identification of operating system, identification of target network topology and target computers, identification of open target ports, assessment of vulnerabilities on target ports, active assessment of vulnerabilities based on information acquired from target computers, quantitative assessment of target network security and vulnerability, and hierarchical graphical representation of the target network, target computers, and vulnerabilities in a test report. The system and method employ minimally obtrusive techniques to avoid interference with or damage to the target network during or after testing.

RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No.11/521,113 filed Sep. 14, 2006 which, in turn, is a divisional of U.S.patent application Ser. No. 10/050,675 filed Jan. 15, 2002, now U.S.Pat. No. 7,152,105, both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to network system security, and more particularlyrelates to systems and methods for automatic detection, monitoring andreporting of network vulnerabilities.

2. Description of the Related Art

The reliability and security of a network is essential in a world wherecomputer networks are a key element in intra-entity and inter-entitycommunications and transactions. Various tools have been used by networkadministrators, government, security consultants, and hackers to testthe vulnerabilities of target networks, such as, for example, whetherany computers on a network can be accessed and controlled remotelywithout authorization. Through this intensive testing, a target networkcan be “hardened” against common vulnerabilities and esoteric attacks.Existing testing systems, however, produce inconsistent results, usetechniques that are unproven or that damage the target network, fail torespond to changing network environments or to detect newvulnerabilities, and report results in difficult to understand,text-based reports.

Well-known network security tools now exist to test network paths forpossible intrusion. From a testing point, simple commands such astraceroute and ping can be used to manually map a network topography,and determine roughly what network addresses are “alive” with a computer“awake” on the network (i.e., determine which computers are on and areresponding to network packets). A tool such as a port scanner can beused to test an individual target computer on the target network todetermine what network ports are open. If open ports are found, theseports may provide access for possible intrusion, and potentiallyrepresent a vulnerability that can be exploited by a malicious hacker.

Some suites combining various network tools attempt to follow aquasi-automated process to test target computers on a target network.These suites provide variations on the tools described above, andprovide long-form text-based output based on the outcome of thistesting. The output of these security tests are extremely technical, andrequire extensive knowledge of network communications in order tointerpret and provide advice based on the results. Thus, these partiallyautomated suites do not provide comprehensive security to an entityseeking to “harden” its network.

Further, some security suites actually risk substantial damage to thetarget network. For example, while the use of malformed network packetsto test a target computer can provide extensive information from thetarget and feedback on the security of the target, these malformedpackets can destabilize the target computer in unpredictable ways. Thissometimes results in a short-term loss of information to the targetcomputer or, in more serious cases, a complete crash of the targetcomputer operating system or hardware.

In other cases, the testing method used by existing suites is notreliable. If a network port scanning method employed on a targetcomputer is, for example, 80% accurate over time, then a complete testof all 2¹⁶ ports on a single computer may result in approximately 13,000ports incorrectly identified as potentially running vulnerable services.Over an entire target network, such “false positives” make it virtuallyimpossible to determine the true security level of the target network.

Existing testing methods lack a standard, quantitative method forobjectively comparing the security of a target network or targetcomputer to other systems. Typically, a target network or targetcomputer is ranked only as “high risk,” “medium risk,” or “low risk.”However, such a three-tier system alone provides very little substantivefeedback or comparative information about changes in the network overtime, the relative weight of different vulnerabilities in determiningthe resulting risk level, or objective assessments of network securityamong otherwise heterogeneous network environment.

SUMMARY OF THE INVENTION

The present invention solves these problems and more through acomprehensive network vulnerability testing and reporting method andsystem. Specifically, the testing system features include a selectedcombination of: (1) a non-destructive identification of target computeroperating system; (2) a multiple-tier port scanning method fordetermination of what network addresses are active and what ports areactive at those addresses; (3) a comparison of collected informationabout the target network with a database of known vulnerabilities; (4) avulnerability assessment of some vulnerabilities on identified ports ofidentified target computers; (5) an active assessment of vulnerabilitiesreusing data discovered from previously discovered target computers; (6)an application of a quantitative score to objectively and comparativelyrank the security of the target network; and, (7) reduction of detailedresults of the information collected into hierarchical, dynamic andgraphical representations of the target network, target computers, andvulnerabilities found therein. Other features are foreseen and disclosedherein, as well.

In its preferred embodiment, the testing system operates over a modernmulti-layer packet network such as a corporate intranet or the Internet.The network typically includes one or more computers, where a computerincludes a desktop station running any operating system, a router, aserver, and/or any other networked device capable of sending andreceiving packets through standard interne protocols such as TCP/IP(Transmission Control Protocol/Internet Protocol), UDP (User DatagramProtocol), and the like. The system and method can be run remotely froma monitoring computer outside the target network, or can be run by amonitoring computer included within the target network. The targetnetwork itself is typically defined as an interconnected set ofcomputers, bounded by a specific pre-designated sub-network address,range of IP addresses or sub-addresses, physical network boundaries,computer names or unique identifiers, presence or connection via apre-determined network protocol, and the like. The target computerscomprise all or a portion of the computers found within the targetnetwork. For example, a target computer with a simple connection to aWAN (Wide Area Network) can be tested remotely, as a single peer targetnetwork. In a more complicated example, a distributed network providercan have multiple sub-networks geographically distributed throughout theworld but interconnected via an internal protocol, as a WAN targetnetwork with thousands of target computers.

A target network typically runs on one or more IP-based networkprotocols. Most commonly, the protocol will be TCP/IP and UDP.Similarly, the testing system is typically indifferent to the physicallayer structure and topology of the target network. Only structuralelements such as firewalls or routers that block, reroute, or changepackets will affect the testing system. The testing system, however,attempts to adapt to these structural elements and generally providesaccurate results regardless of physical implementation.

TCP/IP is a fundamental protocol used for packet-based networkcommunications on local area networks, wide area networks, and globaltelecommunications networks such as the Internet. A sample configurationof a TCP/IP SYN (synchronization) packet is shown in Table 1.

TABLE 1 Typical TCP SYN packet Source Port Destination Port SequenceNumber Acknowledgement Number Data Offset Reserved Data Flags WindowChecksum Urgent Pointer Options Padding Data

A computer typically runs on one or more operating systems. Morecommonly, these operating systems include those provided by Microsoft®,such as the Microsoft Windows® family of operating systems, MacOS® fromApple®, various flavors of UNIX including Linux®, NetBSD, FreeBSD,Solaris®, and the like. Additionally, devices on the target network mayinclude router operating systems, mobile communication device operatingsystems, palmtop or handheld operating systems, appliance operatingsystems, set-top box operating systems, gaming operating systems,digital rights management systems, surveillance systems, smart cardtransaction systems, transportation management systems, and the like,that assign unique or temporary network addresses and are capable ofsending and/or receiving traffic from the target network.

Target computers, in one embodiment, are identified by a unique ortemporarily unique IP (Internet Protocol) address, typically in the formA.B.C.D, where each of A, B, C and D represent the Class A, Class B,Class C and Class D sub-networks and each has a value between 0 and 255.Typically, the target network is defined by one or more ranges of IPaddresses controlled by the target network, but may contain additionaltarget computers or target sub-networks connected to the target networktopographically but not part of the predetermined IP range or ranges.

UDP (User Datagram Protocol) is an alternative “connectionless”communications protocol that runs above IP (Internet Protocol). UDPlacks the error correction and receipt acknowledgment features ofconnection-based protocols such as TCP. ICMP (Internet Control MessageProtocol) is another extension of IP which permits controlcommunications (most commonly through a ICMP PING request) between hostson an IP network.

Another aspect of the invention includes non-destructive and relativelynon-intrusive identification of the target operating system of a targetcomputer.

Another aspect of the invention includes parallel testing of multipletarget computers on a target network.

Another aspect of the invention includes an improved testing method todetermine whether particular target computers on a target network arealive.

Another aspect of the invention includes an improved method fordetermining whether a set of commonly used ports are open on a targetcomputer.

Another aspect of the invention includes an improved method for reliablydetermining whether a set of commonly used UDP ports are open or closedon a target computer.

Another aspect of the invention includes a method for associating theports found open on a target computer with a known set ofvulnerabilities.

Another aspect of the invention includes parallel testing of multipleports and multiple target computers simultaneously.

Another aspect of the invention includes active assessment of some knownset of vulnerabilities at a target computer.

Yet another aspect of the invention includes application of an objectivequantitative score to the vulnerabilities found on a target network.

Still another aspect of the invention includes compilation of a dynamic,graphical report representing the network topology, network computers,and network vulnerabilities in a hierarchical report including bothoverview and detail documents.

In one embodiment, the present invention is a system for determining anoperating system of a target computer operably connected to a network.The system comprises (1) first and second data packets, the first andsecond data packets compliant with a protocol supported by the network,the first and second data packets transmitted via the network to thetarget computer; (2) first and second operating system fingerprintscomprising data bits stored in a computer-readable medium, the first andsecond operating system fingerprints associated with a first operatingsystem; (3) a first target computer fingerprint comprising data bitsstored in a computer-readable medium, the first target computerfingerprint including a representation of at least a portion of datareceived in response to the transmission of the first data packet; (4) asecond target computer fingerprint comprising data bits stored in acomputer-readable medium, the second target computer fingerprintincluding a representation of at least a portion of data received inresponse to the transmission of the second data packet; and (5)fingerprint comparison instructions executable by a computer to comparethe first operating system fingerprint and the first target computerfingerprint, to compare the second operating system fingerprint and thesecond target computer fingerprint, and to generate a result indicativeof whether the first operating system was running on the targetcomputer. In a preferred aspect, the invention further comprises: (6) athird data packet, the third data packet compliant with the protocol,the first range of bits of the third data packet representing a thirdparameter value different from the first and second parameter values,the third data packet transmitted via the network to the targetcomputer; (7) a third operating system fingerprint comprising data bitsstored in a computer-readable medium, the third operating systemfingerprint associated with the first operating system, the thirdoperating system fingerprint differing from the first and secondoperating system fingerprints; and (8) a third target computerfingerprint comprising data bits stored in a computer-readable medium,the third target computer fingerprint including a representation of atleast a portion of data received in response to the transmission of thefirst data packet, the comparison instructions executable by a computerto compare the third operating system fingerprint and the third targetcomputer fingerprint before generating the result. In a furtherpreferred aspect, the invention further comprises: (9) fourth, fifth andsixth operating system fingerprints comprising data bits stored in acomputer-readable medium, the fourth, fifth and sixth operating systemfingerprints associated with a second operating system, at least one ofthe fourth, fifth and sixth operating system fingerprints differing froma respective one of the first, second and third operating systemfingerprints; the comparison instructions executable by a computer tocompare the fourth operating system fingerprint and the first targetcomputer fingerprint, to compare the fifth operating system fingerprintand the second target computer fingerprint, to compare the sixthoperating system fingerprint and the third target computer fingerprint,and to generate a second result indicative of whether the secondoperating system was running on the target computer. Preferred aspectsof this embodiment are ones wherein (10) the first parameter value isobtained by setting no bits, the second parameter value is obtained bysetting one bit, and the third parameter value is obtained by settingtwo bits, or (11) wherein the first parameter value is 0, the secondparameter value is 128, and the third parameter value is 128 plus amultiple of 256.

In another embodiment, the present invention is a system for determiningan operating system of a target computer accessible via a network. Thesystem comprises: (1) a plurality of data packets compliant with aprotocol supported by the network, the plurality of data packetstransmitted via the network to the target computer; (2) a firstplurality of operating system fingerprints, each comprising data bitsstored in a computer-readable medium, each associated with a firstoperating system; (3) a plurality of target computer fingerprints, eachcomprising data bits stored in a computer-readable medium, eachincluding a representation of at least a portion of data received inresponse to the transmission of the plurality of data packets; and (4)fingerprint comparison instructions executable by a computer to comparethe first plurality of the operating system fingerprint and theplurality of the target computer fingerprints, and to generate a resultindicative of whether the first operating system was running on thetarget computer. A preferred aspect of the embodiment is one wherein theprotocol is TCP/IP. Another preferred aspect of the embodiment furthercomprises (5) a second plurality of operating system fingerprints, eachcomprising data bits stored in a computer-readable medium, eachassociated with a second operating system, the fingerprint comparisoninstructions comparing the second plurality of the operating systemfingerprints and the plurality of the target computer fingerprints togenerate a second result indicative of whether the second operatingsystem was running on the target computer.

A further embodiment of the present invention is a method fordetermining an operating system of a target computer accessible via anetwork. The method comprises the steps of (1) transmitting to thetarget computer a plurality of data packets compliant with a protocolsupported by the network; (2) generating a plurality of target computerfingerprints, each including at least a portion of data received via thenetwork in response to the transmission of the plurality of datapackets; (3) comparing the plurality of target computer fingerprints toa first set of predetermined operating system fingerprints, each of thefirst set of predetermined operating system fingerprints associated witha first operating system; and (4) generating a result indicative ofwhether the first operating system was running on the target computer.In a preferred aspect the embodiment comprises the further steps of (5)comparing the plurality of target computer fingerprints to a second setof predetermined operating system fingerprints, each of the second setof predetermined operating system fingerprints associated with a secondoperating system; and (6) generating a result indicative of whether thesecond operating system was running on the target computer. Onepreferred aspect of that embodiment is one wherein the protocol isTCP/IP and wherein the value of the MSS option of two of the pluralityof data packets is divisible by 128. Another preferred aspect of thatembodiment is one wherein a first of the plurality of data packets has amaximum segment size option of 0, wherein a second of the plurality ofdata packets has a maximum segment size option of 128, and wherein athird of the plurality of data packets has a maximum segment size optionof 384.

A still further embodiment of the invention is a method for identifyingan operating system of a target computer via a network, the methodcomprising the steps of (1) sending a first data packet to the targetcomputer via the network, the first data packet complying with aprotocol of the network and having a first pattern of bits in a firstrange of bits; (2) generating a first response value representing atleast a portion of data received via the network in response to thesending of the first data packet; (3) sending a second data packet tothe target computer via the network, the second data packet complyingwith the protocol and having a second pattern of bits in a first rangeof bits, the second pattern of bits different from the first pattern;(4) generating a second response value representing at least a portionof data received via the network in response to the sending of thesecond data packet; (5) sending a third data packet to the targetcomputer via the network, the third data packet complying with theprotocol and having a third pattern of bits in a first range of bits,the third pattern of bits different from the first or the secondpattern; (6) generating a third response value representing at least aportion of data received via the network in response to the sending ofthe third data packet; (7) comparing the first response value to a firstpredetermined value associated with a first operating system; (8)comparing the second response value to a second predetermined valueassociated with the first operating system; (9) comparing the thirdresponse value to a third predetermined value associated with the firstoperating system; and (10) generating a value indicative of arelationship between the first operating system and the target computer.A preferred aspect of the embodiment comprises the further steps of:(11) comparing the first response value to a fourth predetermined valueassociated with a second operating system; (12) comparing the secondresponse value to a fifth predetermined value associated with the secondoperating system; and (13) comparing the third response value to a sixthpredetermined value associated with the second operating system. Apreferred aspect of that embodiment is one wherein no bit is set in thefirst pattern of bits, wherein one bit is set in the second pattern ofbits, and wherein two bits are set in the third pattern of bits. Anotherpreferred aspect of that embodiment is one wherein the number of bytesin the second pattern of bits that have at least one bit set is greaterthan the number of bytes in the first pattern of bits that have at leastone bit set, and wherein the number of bytes in the third pattern ofbits that have at least one bit set is greater than the number of bytesin the second pattern of bits that have at least one bit set.

Yet another embodiment of the present invention is a system fordetermining whether a target computer is on a network, the systemcomprising: (1) a first set of port identifiers stored in acomputer-readable medium, each of the first set of port identifiersrepresenting a port used by computers to receive data packets compliantwith a first protocol of the network, each of the first set of portidentifiers representing a port associated with known network services;(2) a first set of data packets, each directed to a port represented byat least one of the first set of port identifiers, each of the first setof data packets compliant with the first protocol and transmitted to thetarget computer via the network; (3) a first set of acknowledgementpackets received via the network in response to the transmission of thefirst set of data packets, and (4) a list of host identifiers, each hostidentifier representing a computer on the network that transmits data inresponse to a packet sent to the respective computer, a host identifierrepresenting the target computer added to the list of host identifiersif the first set of acknowledgment packets indicates a responsiveness ofthe target computer. An alternative preferred aspect of the embodimentfurther comprises: (5a) a second set of port identifiers stored in acomputer-readable medium, each of the second set of port identifiersrepresenting a port used by computers to receive data packets compliantwith a second protocol of the network, each of the second set of portidentifiers representing a port associated with known network services;(6a) a second set of data packets, each directed to a port representedby at least one of the second set of port identifiers, each of thesecond set of data packets compliant with the second protocol andtransmitted to the target computer via the network, at least one of thesecond set of data packets including data associated with the knownnetwork services; (7a) a second set of acknowledgement packets receivedvia the network in response to the transmission of the second set ofdata packets; and (8a) a host identifier representing the targetcomputer added to the list of host identifiers if the second set ofacknowledgment packets indicates a responsiveness of the targetcomputer. A preferred aspect of that embodiment is one wherein the firstprotocol is TCP, wherein the second protocol is UDP, wherein the secondset of acknowledgment packets is a nonzero set of UDP data responsepackets. Another alternative preferred aspect of the embodiment furthercomprises: (5b) a second set of port identifiers stored in acomputer-readable medium, each of the second set of port identifiersrepresenting a port used by computers to receive data packets compliantwith a second protocol of the network, each of the second set of portidentifiers representing a port associated with known network services;(6b) a second set of data packets, each directed to a port representedby at least one of the second set of port identifiers, each of thesecond set of data packets compliant with the second protocol andtransmitted to the target computer via the network, at least one of thesecond set of data packets including data associated with the knownnetwork services; (7b) a second set of acknowledgement packets receivedvia the network in response to the transmission of the second set ofdata packets; and (8b) a host identifier representing the targetcomputer added to a second list of host identifiers if the second set ofacknowledgment packets does not indicate an unresponsiveness of thetarget computer, each of the second list of host identifiersrepresenting a computer not known to be unresponsive. A preferred aspectof that embodiment is one wherein the first protocol is TCP, wherein thesecond protocol is UDP, wherein the second set of acknowledgment packetsis an empty set of ICMP error packets. A further preferred aspect ofeither alternative embodiment further comprises: (9) a third set of datapackets, each directed to a port represented by at least one of thesecond set of port identifiers, each compliant with the second protocol,the third set of data packets transmitted to the target computerthroughout a predetermined maximum latency period; (10) a first responsereceived first in time in response to the transmission of the third setof data packets; (11) a second response received second in time inresponse to the transmission of the third set of data packets, a timeduration between the receipt of the first response and the receipt ofthe second response defining a target computer latency period. A furtherpreferred aspect of the embodiment is one wherein each of the second setof data packets is transmitted continuously to the target computer forthe duration of the target computer latency period.

A still further embodiment of the present invention is a system fortesting the accessibility of a target computer via a network. The systemcomprises: (1) a set of port identifiers stored in a computer-readablemedium, each of the set of port identifiers representing a UDP-compliantport, at least one of the port identifiers representing a portassociated with known network services; (2) a set of UDP-compliant datapackets, each associated with a port represented by at least one of theset of port identifiers, each of the UDP-compliant data packetstransmitted continuously to the target computer for a durationapproximately the same as the latency period of the target computer, atleast one of the UDP-compliant data packets including data associatedwith the known network services; (3) a first list representing computersaccessible via the network, the first list including the target computerif a nonzero set of UDP data response packets is received in response tothe transmission of the data packets; and (4) a second list representingcomputers not known to be inaccessible via the network, the second listincluding the target computer if an empty set of ICMP error packets isreceived in response to the transmission of the data packets.

Another embodiment of the present invention is a method for determiningwhether a target computer is accessible via a network. The methodcomprises the steps of: (1) identifying TCP ports; (2) sending firstdata packets to the TCP ports of the target computer, each of the firstdata packets compliant with TCP; (3) receiving first acknowledgmentpackets in response to the sending of the first data packets; and (4)adding a representation of the target computer to a list representingaccessible computers if the first acknowledgment packets are nonzero. Apreferred aspect of the embodiment comprises the further steps of: (5)identifying UDP ports associated with network services; (6) sendingsecond data packets to the UDP ports of the target computer, at leastone of the second data packets sent continuously to the target computerthroughout a latency period of the target computer, (7) receiving secondacknowledgment packets in response to the sending of the second datapackets; and (8) adding a representation of the target computer to alist representing accessible computers if the second acknowledgmentpackets are nonzero UDP data response packets. A further preferredaspect of the embodiment comprises the further step of: (9) determiningthe latency period of the target computer by measuring the time betweenresponses received in response to packets transmitted to the targetcomputer. A further preferred aspect of the embodiment comprises thefurther step of: (10) adding a representation of the target computer toa list representing computers not known to be inaccessible via thenetwork, the adding performed if the second acknowledgment packetscomprise an empty set of ICMP error packets.

An additional embodiment of the present invention is a method forassessing the vulnerability of a target computer via a network. Themethod comprising the steps of: (1) discovering a set of responsivecomputers on a network by transmitting a set of ICMP packets, a set ofTCP packets and a set of UDP packets to a group of computers on anetwork; (2) detecting services on each of the set of responsivecomputers by transmitting TCP packets to first ports of each of the setof responsive computers and by transmitting UDP packets to second portsof each of the set of responsive computers, the first and second portscommonly used by computers to receive data packets over a network, theTCP packets including data associated with at least one computer-basedservice known to use one of the first ports, the UDP packets includingdata associated with at least one computer-based service known to useone of the second ports; and (3) generating a list of responsive portsusing responses received in response to the transmission of the TCPpackets and the UDP packets. A preferred aspect of the embodimentcomprises the further step of (4) determining an operating system usedby each of the set of responsive computers by comparing predeterminedvalues with portions of responses received from each of the set ofresponsive computers in response to transmission of a plurality ofTCP-compliant packets to each of the set of responsive computers. Afurther preferred aspect of the embodiment comprises the further step of(5) confirming the presence of vulnerabilities on the network byapplying an automated vulnerability script to each responsive portrepresented in the list of responsive ports, each of the automatedvulnerability scripts testing a vulnerability known to be associatedwith a computer configuration comprising a particular responsive portand a particular operating system. A still further preferred aspect ofthe embodiment comprises the further step of: (6) calculating anobjective indicia of security of the network, the calculation based on aweighted summation of confirmed vulnerabilities. A preferred aspect ofthe embodiment comprises the further step of: (7) determining a topologyof the network, the topology determination made by transmitting a set ofICMP packets with varying time to live (TTL) settings and bytransmitting a set of TCP packets with varying TTL settings. Anotherpreferred aspect of the embodiment comprises the further step of: (8)producing a graphical representation of the network, the representationincluding a topological map of the network, a color-based representationof weighted confirmed vulnerabilities, and an association between thegraphical representation and information descriptive of confirmedvulnerabilities and computers on the network.

Another embodiment of the present invention is a method for creating atopological representation of a network. The method comprises the stepsof: (1) identifying responsive computers on the network; (2) obtaining aplurality of sequences of IP addresses by sending to each responsivecomputer a sequence of packets having increasing TTL values, eachsequence of IP addresses representing nodes in the network between asource computer and one of the responsive computers, adjacent IPaddresses in each sequence representing connected nodes, each of thenodes comprising a computer or a router, (3) generating a list of nodestructures, each of the node structures including data representing anode and data indicative of other nodes to which it directly connects,the list representing all IP addresses in the plurality of sequences;(4) determining for each IP address a distance count, the distance countrepresenting a number of nodes between a node having the IP address anda source node; (5) creating a router structure for each node structurethat represents a node comprising a router; (6) associating with each ofthe router structures connection data representative of each connectingnode that connects to no other node except the muter represented by therespective router structure; (7) for each router structure, visuallydepicting a graphical shape spatially related to one or more graphicalshapes corresponding to connecting nodes represented by the connectiondata of the respective router structure; and (8) for each routerstructure, visually depicting a connection between a graphical shapeassociated with the respective router structure and another graphicalshape associated with a different muter structure when distance countsassociated with the IP addresses of routers represented by therespective router structure and the different router structure indicatea direct connection. A preferred aspect of the embodiment comprises thefurther step of (9) testing whether a router represented by a routerstructure and a connecting node represented in connection data comprisetwo network connections of one node. A further preferred aspect of thisembodiment is one wherein the graphical shape representing a router is asphere, and wherein each of the spatially related graphical shapes is asphere orbiting the sphere representing the router.

Yet another embodiment of the present invention is a method forcalculating an objective security score for a network. The methodcomprising the steps of (1) determining a vulnerability valuenumerically representing a combination of known vulnerabilities of anetwork; (2) determining an exposure value numerically representing acombination of accessible ports of computers on the network; and (3)deriving a score by combining the vulnerability value and the exposurevalue. A preferred aspect of this embodiment is one wherein thecombination of known vulnerabilities is a summation of weighted numericexpressions of particular vulnerabilities, the weighting based on anease of exploitation ranking and on an access granted ranking for eachvulnerability.

Still another embodiment of the present invention is a method forconducting an automated network vulnerability attack, the methodcomprising the steps of: (1) selecting a set of vulnerability attacksfor each responsive computer on a network, each selected vulnerabilityattack for each responsive computer designed to expose a vulnerabilityassociated with ports of the respective computer known to be accessibleand also associated with an operating system used by the respectivecomputer; (2) encoding the set of vulnerability attacks such that eachis represented in a database by a unique identifier; (3) representingeach of the set of vulnerability attacks using instructions of anautomated scripting language; and (4) executing the vulnerabilityattacks by processing the instructions with a computer.

One more embodiment of the present invention is a hierarchical networkvulnerability report. The report comprises: (1) a first report levelcomprising: (a) an objective score representing the security of thenetwork; and (b) a graphical representation of a network topology,including a graphical representation of computers accessible via thenetwork and a color-based graphical representation of the vulnerabilityof at least some of the computers; and (2) a second report levelcomprising: (a) a textual list describing the computers and theirassociated vulnerabilities; and (b) an exposure report describingaccessible ports and services of the computers.

An additional embodiment of the present invention is a vulnerabilityassessment language. The vulnerability assessment language comprises:(1) a set of programming language statements used to create executablescripts, the scripts executed in a thread-safe execution architecturewherein all variables are stack variables and wherein a parse tree istreated as a read-only data structure; (2) a set of special scalar datatypes interchangeable with an integer data type in expressions, each ofthe set of special scalar data types having a set of constant valuesconfigured to support vulnerability assessment operations embodied inscripts; (3) a set of native objects declared in a metascope owning ascript scope to make available the native objects to executable scripts,the native objects facilitating network communication, providingcallable member functions for building lists of unique ports anddirecting script execution to certain hosts, and providing IP addressesfor scripts; and (4) a vulnerability object behaving to copy itself intoa global data area where other scripts may access its information tocompromise another machine, facilitating the use by one script ofvulnerability data discovered by a different script.

A further embodiment of the present invention is a method for automatedapplication of a known vulnerability on a target computer. The methodcomprises the steps of: (1) providing a database of knownvulnerabilities, the database including a data object; (2) providing anexecutable script, the executable script associated with the dataobject; (3) applying the executable script to the target computer, thescript performing the known vulnerability on a port of the targetcomputer; and (4) returning a value representing at least one of thesuccess, failure or other outcome of the executable script A stillfurther embodiment of the present invention is a method for automatedapplication of known vulnerabilities to target computers of a network.The method comprises the steps of (1) providing a database of knownvulnerabilities; (2) providing a set of executable scripts, eachexecutable to apply a known vulnerability to a specified targetcomputer; (3) executing first executable scripts to applyvulnerabilities on specified target computers; (4) monitoring returnvalues representing a success, failure or other outcome of each of thefirst executable scripts; and (5) generating a report using the returnvalues, the report representing a security level of the network. Onepreferred aspect of this embodiment comprises the further step of (6)identifying execution time intervals wherein execution of the firstexecutable scripts commences at the beginning of each of the timeintervals and pauses at the end of each of the time intervals, until allof the first executable scripts have executed. A preferred aspect of theembodiment comprises the further step of (7) automatically repeating theexecution of the first executable scripts when the execution of thefirst executable scripts is completed. Another preferred aspect of theembodiment comprises the further steps of: (8) generating a report uponeach completed execution of the first executable scripts; and (9)calculating a security trend for the network by comparing a plurality ofthe reports. An alternative preferred aspect of the embodiment comprisesthe further step of (10) executing second executable scripts to applyvulnerabilities to a second network of computers during the execution ofthe first executable scripts. Another preferred aspect of the embodimentis one wherein the second network is a subset of the network. Stillanother preferred aspect of the embodiment is one wherein the firstexecutable scripts are configured to apply vulnerabilities to a firstport of all of the target computers before applying vulnerabilities to asecond port of all of the target computers. An additional preferredaspect of the embodiment comprises the further step of allocating aplurality of packet slots, each packet slot permitting asynchronoustransmission of a packet by one of the executable scripts.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are described below inconnection with the attached drawings in which:

FIG. 1 illustrates one embodiment of a target network;

FIG. 2 illustrates one embodiment of a target computer on the targetnetwork;

FIG. 3 illustrates one embodiment of a comprehensive testing method;

FIG. 4 illustrates one embodiment of the operating system identificationmethod;

FIG. 5 illustrates one example embodiment of the TCP SYN packet used inthe operating system identification method of FIG. 3;

FIG. 6 illustrates one embodiment of first phase scanning to determinewhat target computers are alive;

FIG. 7 illustrates one embodiment of second phase scanning to determinewhat ports are open on a target computer;

FIG. 8 illustrates one embodiment of active assessment of avulnerability of a target computer on a target network;

FIG. 9 illustrates one embodiment of a methodology for determining thesecurity score for a target network;

FIG. 10 illustrates one embodiment of a hierarchical security report,including a graphical representation of network topology and networkvulnerabilities; and

FIG. 11 illustrates a second embodiment of a hierarchical securityreport in greater detail.

FIG. 12 illustrates a second embodiment of the comprehensive testingmethod.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

I. Basic Implementation, Structure and Control Language

FIG. 1 illustrates one embodiment of a target network. The networksecurity system 100 of the present invention is, in one embodiment, atleast one Intel-based server running on a Windows 2000 operating system,although any computer system or operating system capable of handling anIP network and capable of large-scale data processing can be used. Thenetwork security system 100 may be outside the target network 102 orinside the target network (not shown). In either case, the system 100 isconnected to the target network 102 through a network such as theInternet, via one or more nodes 104. The target network 102, in oneexample, consists of an intranet with a central intranet hub 106. Thetarget network 102 further includes a firewall 108 which blocks someincoming traffic to or outgoing network traffic leaving the targetnetwork 102. The target network further comprises a number of hosts 110,defined as within a predetermined range of Internet Protocol (IP)addresses. In some cases, external hosts 112 may lie outside the targetnetwork but may nonetheless be connected to the target network 102.

FIG. 2 illustrates one embodiment of a target computer on the targetnetwork. In general, a host IP address represents a target computer, asmore generally defined below, if the address is in use by the targetnetwork. In a simplified representation of a target computer 200 at ahost 110, the target computer 200 is running an operating system 202.The operating system preferably contains at least one network TCP/IPstack 204 to provide packet transport, preferably including an interfaceto provide raw socket 206 connections between the target computer 200and the network. The physical connection to the network 208 is provided,in one embodiment, by a Network Interface Card (NIC) 210. On an IPnetwork, a packet can be received at any one of 65,536 logical ports 212at the target computer 200. Similarly, any number of network services214 can be provided.

FIG. 3 illustrates one embodiment of a comprehensive testing method inaccordance with embodiments of the present invention. FIG. 3 presents anoverview of the method. Additional details of the method are set forthbelow in connection with FIGS. 4-11.

In a first step or routine 310 in FIG. 3, the testing method defines thetarget network and creates a scan list of IP addresses. The scan list isstored in a scan list database 312. Then, in a routine 314, the methodobtains a first batch of IP addresses from the scan list database 312and begins a detailed analysis of the target network by performing ahost discovery routine that begins in a block 320.

The host discovery routine comprises an ICMP host discovery routine 322,which will be described in more detail below. During the ICMP hostdiscovery routine 322, the method pings the target computers identifiedby the present batch of IP addresses. Based on the responses or lack ofresponses, the ICMP host discovery routine 322 is able to determine thatcertain target computers are “live” or “probably live,” and theassociated IP addresses are added to a respective live database 324 orprobably live database 326 accordingly.

After completing the ICMP host discovery routine 322, the methodperforms a decision routine 328 wherein the method determines whetherall the IP addresses in the current batch of IP addresses have beendiscovered (i.e., whether all the IP addresses have been assigned to thelive database 324 or the probably live database 326. If any IP addresshas not been discovered, the method proceeds to a TCP host discoveryroutine 330, which will be described in more detail below. During theTCP host discovery routine 330, the method sends TCP packets to theremaining target computers identified by the present batch of IPaddresses. Based on responses or lack of responses, the TCP hostdiscovery routine 330 is able to determine that certain ones of theremaining target computers are “live” or “probably live,” and theassociated IP addresses are added to a respective live database 324 orprobably live database 326 accordingly.

After completing the TCP host discovery routine 330, the method performsa decision routine 332 wherein the method determines whether all the IPaddresses in the current batch of IP addresses have been discovered(i.e., whether all the IP addresses have been assigned to the livedatabase 324 or the probably live database 326. If any IP address hasnot been discovered, the method proceeds to an intelligent UDP hostdiscovery routine 334, which will be described in more detail below.During the intelligent UDP host discovery routine 334, the method sendsUDP packets to the remaining target computers identified by the presentbatch of IP addresses. Based on responses or lack of responses, theintelligent UDP host discovery routine 334 is able to determine thatcertain ones of the remaining target computers are “live” or “probablylive,” and the associated IP addresses are added to a respective livedatabase 324 or probably live database 326 accordingly.

After completing the intelligent UDP host discovery routine 334, themethod performs a decision routine 336 wherein the method determineswhether all the IP addresses in the current batch of IP addresses havebeen discovered (i.e., whether all the IP addresses have been assignedto the live database 324 or the probably live database 326. If any IPaddress has not been discovered, the method, in one embodiment, proceedsto an intensive UDP host discovery routine 338, which will be describedin more detail below. During the intensive UDP host discovery routine338, the method sends additional UDP packets to the remaining targetcomputers identified by the present batch of IP addresses. Based onresponses or lack of responses, the intensive UDP discovery routine 338is able to determine that certain ones of the remaining target computersare “live” or “probably live,” and the associated IP addresses are addedto a respective live database 324 or probably live database 326accordingly. The intensive UDP host discovery routine 338 is optionaland may not be included in all embodiments.

After completing the intensive UDP host discovery routine 338, themethod preferably proceeds to a service discovery routine that begins ina block 340. Alternatively, in certain embodiments, the foregoing hostdiscovery routines 322, 330, 334, 338 are advantageously repeated todetermine whether additional IP addresses corresponding to targetcomputers can be assigned to the live database 324 and the probably livedatabase 326. In such alternative embodiments, the method repeats thehost discovery routines a maximum of a predetermined times beforecontinuing to the service discovery routine 340. Those IP addresses forwhich no response is received by any method are, in one embodiment,added to a dead list 339 of hosts.

In the service discovery routine, the method performs a TCP servicediscovery routine 342, which will be described in more detail below. Inthe TCP service discovery routine 342, the method sends TCP packets toselected ports of the discovered target computers in the live list 324and the probably live list 326 and monitors the responses. Based on theresponses or lack of responses, the TCP discovery routine 342 addsinformation regarding open ports of the target computers to a targetcomputer database 344.

After performing the TCP service discovery routine 342, the methodperforms a UDP service discovery routine 346, which will be described inmore detail below. In the UDP service discovery routine 346, the methodsends UDP packets to selected ports of the discovered target computersin the live list 324 and the probably live list 326 and monitors theresponses. Based on the responses or lack of responses, the UDPdiscovery routine 346 adds information regarding open ports of thetarget computers to the target computer database 344. In alternativeembodiments, the TCP service discovery routine 342 and the UDP servicediscovery routine 346 are advantageously repeated a limited number oftimes to determine whether additional open ports are discovered.

After completing the UDP service discovery routine 346 (or aftercompleting the routine a limited number of times), the method proceedsto an operating system (OS) identification routine 350 wherein themethod determines the type and version of operating system present oneach of the live computers having open ports. As will be described inmore detail below, the method sends two or more (preferably three) RFCcompliant TCP packets to the target computers. The TCP packets havepredetermined data in at least one selected field. Each target computerresponds to each of the TCP packets. The response information from eachcomputer is treated as a “fingerprint” for each computer. Thefingerprint from each computer is compared with fingerprints infingerprint database 352, and the results of the comparisons are used toidentify the target computers with high degrees of accuracy.

After completing the operating system identification routine 350 for thetarget computers, the method proceeds to a traceroute routine thatbegins in a block 354. In the traceroute routine, the method firstperforms an ICMP traceroute routine 356 in which the method uses ICMPtracerouting techniques, described in more detail below. In particular,the method sends a plurality of ICMP echo request packets to the targetcomputer with varying TTL (time to live) values in the TCP/IP header.The method creates a network topology based on the known TTL value, thenumber of “hops” between the system and the target computer, and therouter/host at each “hop.” The information from the ICMP tracerouteroutine 356 is added to a network map database 358. When all packetssent have either arrived, failed to arrive, or timed out, the traceroutestep is completed for that target computer. The ICMP traceroute stepsare repeated until a complete trace is received or a selectedpredetermined maximum number of passes is completed.

After completing the predetermined number of ICMP traceroute passes, themethod proceeds to a decision routine 360 wherein the method determineswhether the trace of the target computer is complete or incomplete. Ifthe trace is incomplete, the method proceed to a TCP traceroute routine362. Otherwise, the method bypasses the TCP traceroute routine andproceeds directly to a vulnerability assessment routine 364.

As described in more detail below, the TCP traceroute routine 362 workssimilarly to ICMP traceroute routine 354, except that TCP SYN packetsare sent to the target computers. As with ICMP tracerouting, the TTLvalue in each SYN packet is incrementally increased, and the return ofICMP unreachable packets and SYN ACK packets is monitored for all “hops”between the scanning system and the target host. Through the combinationof ICMP tracerouting and TCP tracerouting, a complete map to each targetcomputer, and collectively a relatively complete map of the targetnetwork topology is advantageously created and stored in the network mapdatabase 358.

After completing the TCP traceroute routine 362, the method proceeds tothe vulnerability assessment routine 364. As described in more detailbelow, in the vulnerability assessment routine 364, the method executesvulnerability scripts that apply known vulnerabilities to open ports ofthe live target computers to determine whether the ports of the targetcomputers exhibit the potential vulnerabilities. The method usesinformation stored in a known vulnerability database 366 to select thevulnerability scripts to executes for each active port. Informationcollected from vulnerable target computers is advantageously stored tothe target computer database 344.

In one embodiment, the vulnerability assessment routine 364 preferablyonly performs vulnerability checks associated with the identifiedoperating system and open ports of the target computer as determined bythe operating system identification routine 350 and service discoveryroutine 340. If the operating system is not conclusively identified,typically the routine runs all known vulnerabilities for the open portsof the target computer.

In one embodiment, the method proceeds to an active assessment routine365. As further described in detail below, the active assessment routine365 uses information collected from target computers in thevulnerability assessment routine 364 to execute further vulnerabilityscripts to open ports of the live target computers. Specifically, theactive assessment routine 365 reuses known vulnerabilities andinformation collected from target computers to continue to determinewhether the ports of the target computers exhibit potentialvulnerabilities, using information from the known vulnerability database366 and information collected in the target computer database 344.

After completing the active assessment routine 365, the method proceedsto a decision routine 368 to determine whether the method has analyzedall the potential target computers. In particular, in the decisionroutine 368, the method determines whether the last batch of IP addresshas been analyzed. If further batches of target computers remain to beanalyzed, the method proceeds to the routine 314 to obtain the nextbatch of IP addresses. Otherwise, the method proceeds to a scoringroutine 370.

In the scoring routine 370, described in more detail below, the methodestablishes a vulnerability score for each target computer and for thenetwork based on the results of the active assessment and based on thevulnerability information in the known vulnerability database 366. Themethod then proceeds to a reporting routine 372, also described in moredetail below, wherein the method reports the results of the scanning,active assessment and scoring.

The method can be advantageously repeated continuously on a targetnetwork, and can be scheduled into pre-determined scanning window timeperiods for execution of the method over time. For example, in preferredembodiments, the method is scheduled to scan during off-peak hours whenthe network is less likely to be less heavily used. In particularlypreferred embodiments, the method is interruptible at the end of awindow of off-peak hours and resumes where it paused at the beginning ofthe next off-peak window. In particularly advantageous embodiments, themethod operates on multiple target networks concurrently by threading toshare network resources.

II. Non-Destructive Operating System Identification

Vulnerability of and access to a target computer may be heightened byknowing which particular operating system is running on the computer.Identifying a target computer's operating system can be accomplished byexamining the operating system's response to a data packet it receivesover the network. The forms of the packets and the responses to thepackets are generated in accordance with network protocols. The writtendefinitions of the protocols used for communications on the Internet areset forth in Internet Request for Comment (RFC) documents. For example,the TCP/IP protocol is defined in part in RFC 793, incorporated hereinby reference, and contains a standard model for TCP packetcommunications over a network. While virtually every operating systemincludes a TCP/IP stack, each TCP/IP stack is implemented in a slightlydifferent manner. Thus, known responses from a TCP/IP stack unique to aparticular operating system can serve as a “fingerprint” to determinethe target computer's actual operating system.

Operating system detection traditionally has been performed by sendingout a combination of RFC-compliant and non-RFC compliant TCP packets.The traditional system then collects the unique, non-standard responsefrom the target computer and maps the response to a known database ofTCP/IP stacks and related operating systems. However, this method tendsto be inaccurate, highly dependent on the particular packet shape andTCP/IP stack of the target computer, and requires a large number ofpackets to identify the target operating system with any degree ofreliability. This method may trigger security or firewall alarms at thetarget computer, and, more seriously, this method may interfere with oractually crash the target computer, in large part due to the non-RFCcompliant packets sent to the target.

The present system typically employs a unique set of new features tomaximize the accuracy of operating system detection while minimizingintrusiveness and interference with operations of the target computer.In one embodiment, the invention sends RFC-compliant TCP “SYN”(synchronization) packets to a target computer. The use of RFC-compliantTCP packets advantageously reduces the probability that the detectionpackets are blocked by a router or firewall, and greatly reduces theprobability that the detection packets will cause damage or crashes atthe target computer. In one particularly preferred embodiment, theinvention uses just three RFC-compliant TCP packets. Thus, networkstrain is significantly reduced during detection of the operatingsystems of a large number of target computers on a target network.

In one embodiment, the first packet sent is a completely standard TCPSYN to an open port on the target computer. The MSS (maximum segmentsize) option in the options field of the first packet is set to 0 (i.e.,no bits set in the MSS option). See FIG. 5. When an acknowledgementpacket, a SYN ACK packet, is received by the detection system from thetarget computer, certain bits from the packet are saved by the system.In one embodiment, for example, the TCP advertised window, TTL(time-to-live), options, flags, and the DF (don't fragment) fields aresaved to a first fingerprint.

In this embodiment, a second packet is then sent. The second TCP SYNpacket is again a standard TCP SYN packet; however, the MSS option isset to 128 in the second packet (corresponding to the setting of asingle bit in the MSS option). Portions of the response SYN ACK from thetarget computer (preferably the TCP advertised window, TTL, and DF bits)are again saved to a second fingerprint. Finally, a third TCP SYN packetis sent. The third packet is also a standard TCP SYN packet; however,the MSS option is set to 384 in the third packet (corresponding to thesetting of two bits in the MSS option). Again, portions of the responseSYN ACK from the target computer (preferably the TCP advertised window,TTL, and DF bits) are once again saved to a third fingerprint.

In one embodiment, the fingerprint is saved in the following format:

AW_(MSS=0):AW_(MSS=128):AW_(MSS=384):TTL:DF:OS

where, for example,

-   -   AW=TCP advertised window    -   MSS=TCP Options Maximum Segment Size    -   TTL=TCP Options Time to Live    -   DF=TCP Options Don't Fragment Flag, and    -   OS=Operating System identification.

In another embodiment, the fingerprint is saved in the following format:AW_(MSS=0):AW_(MSS=128):AW_(MSS=384):OPT_(MSS=384):OPT_(MSS=0):OPT_(MSS=128):TTL:DF:FL:OSwhere, for example,

-   -   OPT=TCP Options Bytes, and    -   FL=TCP Flags.

The fingerprints are then compared to a known database of fingerprintsassociated with various operating systems and operating system versions.Known fingerprints can be compiled through application of the abovemethodology to various target computers known to have a particularoperating system before testing. For example, testing of known computersrunning various versions of the Solaris® operating system provide thefollowing operating system fingerprints:

TABLE 2 Sample OS Fingerprints for Solaris and BSD operating systems AW₀AW₁₂₈ AW₃₈₄ OPT₀ OPT₁₂₈ OPT₃₈₄ TTL DF Flags OS 83E8 8380 8400 0204021802040080 02040180 FF 0 SA-- Solaris 2.6 6050 6000 6000 02040564 0204056402040564 40 0 SA-- Solaris 2.7 6050 6000 6000 020405B4 020405B4 020405B440 0 SA-- Solaris 8 4000 4000 4080 — — — 64 0 — OpenBSD 2.x 4000 40004000 — — — 64 0 — NetBSD 1.4.2

While more than one OS fingerprint may be associated with each operatingsystem, collisions between fingerprints of distinct operating systemshave been found to be highly unlikely. Tables can be compiled for otheroperating systems similar to that shown in Table 2. As operating systemversions and popularity change over time, the fingerprint database isadvantageously regularly updated to account for patches, versionchanges, and new operating systems. The fingerprint style shown above isonly one embodiment of such a database, and any efficient method tostore the operating system fingerprint can be used, based upon the TCPoptions altered, number of packets typically sent to a target computer,other TCP fields stored for recognition, and identification field usedto represent a particular operating system and version, and the like. Inone example, a unique data string for a particular operating system iscompressed and stored using a digest algorithm such as MD5, and thelike. For further example, perfect matching of fingerprints is notrequired: a system may employ a percentage match, such as, for example,90% similarity between two fingerprints, as sufficient to identify atarget computer as having a particular operating system or at leastbeing in particular family of operating systems.

Below is an example exchange of packets when performing an OSidentification. Three standard TCP SYN packets are sent to the remotehost. The first packet is a SYN packet with no data and no IP or TCPoptions. Packet 2 is also a TCP SYN packet but a TCP Maximum SegmentSize of 128 in the TCP options field is set. The third and final packetis again a TCP SYN packet but a TCP Maximum Segment Size of 384 is setin the TCP options field.

As noted above, by analyzing the replies from the 3 packets, afingerprint is assembled that appears in a textual format as follows:

window1:window2:window3:options1:options2:options3:ttl:dontfrag:flags

where,

-   -   window1=is the TCP window size received from the 1st response    -   window2=is the TCP window size received from the 2nd response    -   window3=is the TCP window size received from the 3rd response    -   options1=the option bytes received from the 1st response    -   options2=the option bytes received from the 2nd response    -   options3=the option bytes received from the 3rd response    -   ttl=is the IP TTL field from the 1st response    -   dontfrag=is the IP dontFragment bit from the 1st response, and    -   flags=are single character representations of the TCP flags from        1st response.    -   In the example TCP packets shown below, the resultant        fingerprint looks like this:

40E8:4000:4080:020405B4:020405B4:020405B4:80:1:SA—

From this, the fingerprint is compared to a database of known operatingsystem fingerprints in order to find the closest match that willidentify the remote operating system. In this example, three example TCPpackets sent and three example TCP packets returned are shown below:

  ----------  Packet 1 send  TCP   Source port: 272   Destination port:80   Sequence: 0x01100000 (17825792)   Acknowledgement: 0x00000000 (0)  Header length: 0x05 (5) - 20 bytes   Flags: SYN    URG: 0    ACK: 0   PSH: 0    RST: 0    SYN: 1    FIN: 0   Window: 0x0040 (64)  Checksum: 0x4518 (17688) - correct   Urgent Pointer: 0x0000 (0)   TCPOptions: None   Data length: 0x0 (0) -----  Packet 1 reply  TCP   Sourceport: 80   Destination port: 272   Sequence: 0x659A2C81 (1704602753)  Acknowledgement: 0x01100001 (17825793)   Header length: 0x06 (6) - 24bytes   Flags: SYN ACK   URG: 0   ACK: 1   PSH: 0   RST: 0   SYN: 1  FIN: 0   Window: 0xE840 (59456)   Checksum: 0x9A47 (39495) - correct  Urgent Pointer: 0x0000 (0)   TCP Options   Maximum Segment Size: 0x5B4(1460)   Data length: 0x0 (0) -----  Packet 2 send  TCP   Source port:528   Destination port: 80   Sequence: 0x03100000 (51380224)  Acknowledgement: 0x00000000 (0)   Header length: 0x07 (7) - 28 bytes  Flags: SYN   URG: 0   ACK: 0   PSH: 0   RST: 0   SYN: 1   FIN: 0  Window: 0x0040 (64)   Checksum: 0x1E8A (7818) - correct   UrgentPointer: 0x0000 (0)   TCP Options   Maximum Segment Size: 0x80 (128)  Data length: 0x0 (0) ------  Packet 2 reply  TCP   Source port: 80  Destination port: 528   Sequence: 0x659ABB23 (1704639267)  Acknowledgement: 0x03100001 (51380225)   Header length: 0x06 (6) - 24bytes   Flags: SYN ACK   URG: 0   ACK: 1   PSH: 0   RST: 0   SYN: 1  FIN: 0   Window: 0x0040 (64)   Checksum: 0x098D (2445) - correct  Urgent Pointer: 0x0000 (0)   TCP Options   Maximum Segment Size: 0x5B4(1460)   Data length: 0x0 (0) -------  Packet 3 send  TCP   Source port:784   Destination port: 80   Sequence: 0x05100000 (84934656)  Acknowledgement: 0x00000000 (0)   Header length: 0x07 (7) - 28 bytes  Flags: SYN    URG: 0    ACK: 0    PSH: 0    RST: 0    SYN: 1    FIN: 0  Window: 0x0040 (64)   Checksum: 0x1A8A (6794) - correct   UrgentPointer: 0x0000 (0)   TCP Options    Maximum Segment Size: 0x180 (384)  Data length: 0x0 (0) ----------  Packet 3 reply  TCP   Source port: 80  Destination port: 784   Sequence: 0x659B732B (1704686379)  Acknowledgement: 0x05100001 (84934657)   Header length: 0x06 (6) - 24bytes   Flags: SYN ACK    URG: 0    ACK: 1    PSH: 0    RST: 0    SYN: 1   FIN: 0   Window: 0x8040 (32832)   Checksum: 0x4E04 (19972) - correct  Urgent Pointer: 0x0000 (0)   TCP Options    Maximum Segment Size:0x5B4 (1460)   Data length: 0x0 (0) ------------

While any number of iterations of the fingerprints described above canbe derived for a target computer, it has been determined that threefingerprints provide the most accurate identification of operatingsystem without undue repetitiveness. Similarly, while other TCP optionsflags may be altered to detect target operating systems, it has beenfound that alteration of the TCP advertised window, over a plurality oftest SYN packets, is most effective, preferably with three test SYNpackets with TCP option MSS values of 0, 128 and 384 respectively.Furthermore, alteration of the MSS value in the TCP advertised window isalso less likely to interfere with target computer operation thanalteration of other values in the packets.

The foregoing operating system identification method is summarized inFIG. 4. As described above, in accordance with the method of FIG. 4, anetwork security system 410 first sends a first RFC compliant TCP SYNpacket to a target computer 412 via a first packet transmissionrepresented by a line 420. The first TCP SYN packet has the TCP OptionsMaximum Segment Size (MSS) set to a value of 0 (i.e., all bits cleared).The target computer 412 responds to the first TCP SYN packet with afirst SYN ACK packet represented by a line 422. As discussed above, atleast a portion of the information included in the first SYN ACK packetreceived from the target computer 412 is determined by data in theTCP/IP stack within the target computer 412, and the data is determined,at least in part, by the particular operating system running on thetarget computer 412.

The network security system 410 next sends a second RFC compliant TCPSYN packet to a target computer 412 via a second packet transmissionrepresented by a line 430. The first TCP SYN packet has the TCP OptionsMaximum Segment Size (MSS) set to a value of 128 (i.e., bit 7 set). Thetarget computer 412 responds to the second TCP SYN packet with a secondSYN ACK packet represented by a line 432. As discussed above, at least aportion of the information included in the second SYN ACK packetreceived from the target computer 412 is also determined by data in theTCP/IP stack within the target computer 412, and the data is determined,at least in part, by the particular operating system running on thetarget computer 412.

Preferably, the network security system 410 next sends a third RFCcompliant TCP SYN packet to a target computer 412 via a third packettransmission represented by a line 440. The first TCP SYN packet has theTCP Options Maximum Segment Size (MSS) set to a value of 384 (i.e., bits7 and 8 set). The target computer 412 responds to the third TCP SYNpacket with a third SYN ACK packet represented by a line 442. Asdiscussed above, at least a portion of the information included in thethird SYN ACK packet received from the target computer 412 is alsodetermined by data in the TCP/IP stack within the target computer 412,and the data is determined, at least in part, by the particularoperating system running on the target computer 412.

Together, the information in the three SYN ACK packets received by thenetwork security system 410 from the target computer 412 in response tothe TCP SYN packets comprise a fingerprint that is compared with thefingerprint database 352 described above in connection with FIG. 3.

FIG. 5 illustrates one example embodiment of the TCP SYN packet 500 usedin the operating system identification method of FIG. 3. On a higher(IP) level, the packet typically provides source and destinationInternet Protocol addresses and unique network addresses (not shown). Onthe TCP level, the packet includes the source port 510 from which thepacket was sent, and the destination port 512 on the target computer towhich the packet is destined. The 32 bit sequence number 514 describesthe starting point of the data contained in the packet in the datawindow, and the 32 bit acknowledgement number 516 contains the last bytereceived by the target computer. Data offset 518 and a reserved section520 are also part of the packet.

The TCP flags 522 denote important information about the packet. Inparticular, SYN denotes the first packet in a new stream, and space inthe sequences 514 and 516 is typically reserved for SYN flags besidesthe single bit in the TCP flags region 522. The window 524 describes howmuch data may be transferred into the buffer at one of the end pointcomputers in the TCP packet communication. The checksum 526 and urgentpointer 528 are included. The TCP options 530 typically include amaximum segment size. After packet padding 532, the actual data 534carried by the packet is attached.

III. Multi-Tier Port Scanning for Target Computer Identification andTarget Port Identification

Port scanning is an essential tool for ensuring network security.Typically, a would-be intruder will apply a port scanner to a chosentarget computer to attempt to find open ports. Through these open ports,the intruder may hope to obtain access to the target computer throughknown or unknown vulnerabilities. In the network security context,applying an ordinary port scanner to all 2¹⁶ (65,536) ports on eachtarget computer on a target network may significantly drain networkresources, take an impracticable amount of time, and not provide anaccurate accounting of actual vulnerabilities of target computers.

In one embodiment, the present system employs an iterated port scanningsystem with at least two phases of operation: host discovery and servicediscovery. For a particular set of IP address ranges in the targetnetwork (the “scan list”), host discovery determines which IP addressesrepresent live target computers (i.e., computers that respond to networkpackets) and adds each such address to the “live list” determines whichIP addresses represent computers that are partially responsive, asdiscussed below, and adds each such address to the “potentially livelist;” and determines which IP addresses represent computers that arenon-responsive, and adds each such address to the “dead list.” In theservice scan, each target computer reported as live in the hostdiscovery phase is subjected to scanning of a known set of ports likelyto be open to traffic.

A. Host Discovery

As described in more detail below, the host discovery phase applies one,two or three distinct tests to each IP address on the scan list.Preferably, the scan list is scanned in batches, where each batch of IPaddresses is scanned in parallel (as described in more detail below) toidentify host computers (i.e., live target computers).

i. First Test (ICMP Ping Request)

In a first host discovery test, a standard ICMP ping request is sent toeach target computer. If a response is received, the target computer isremoved from the scan list and placed on the live list. In oneembodiment, this entails sending out an ICMP echo request packet to eachhost. Multiple ICMP packets can advantageously be sent out in parallelto more than one IP address in a batch. Typically, the system waitsuntil an ICMP echo reply is received from all IP addresses in the batchor the ICMP echo request is timed out. As a result of this process, foreach batch of IP addresses on the scan list, a list of IP addresses thatresponded to the ICMP echo request is removed from the scan list andplaced on the live list.

ii. Second Test (Sending TCP Packets)

If no response is received from one or more IP addresses on the list inthe first test, a set of TCP packets (either single SYN packets or fullTCP connection sequences (“TCP full connect”)) are sent to the remainingtarget computers in the scan list as a second host discovery test.Specifically, a list of “TCP discovery ports” is selected in oneembodiment. The selection is based on the TCP ports that are most likelyto be open. The TCP discovery port list is advantageously relativelyshort, and preferably includes well known service ports such as HTTP(hypertext transfer protocol), SMTP (simple mail transfer protocol) andthe like. One non-exclusive example embodiment of a TCP host discoverylist is shown in Table 3.

TABLE 3 Sample TCP Discovery List Service Port FTP 21 SSH 22 Telnet 23SMTP 25 HTTP 80, 81, 8000 POP3 110 NetBIOS 139 SSL/HTTPS 443 PPTP 1723

Other common ports can be added or removed from the list, and the list,for example, can be tailored to specific network environments wherecertain ports are more likely to be in use than others. In this example,File Transfer Protocol (FTP), Secure Shell (SSH), Telnet, Simple MailTransfer Protocol (SMTP), HyperText Transfer Protocol (HTTP), PostOffice Protocol (POP3), NetBios, Secure Sockets Layer (SSL), andPoint-to-Point Tunneling Protocol (PPTP) are advantageously used.

In one embodiment, a standard TCP SYN packet is sent to some or all ofthe ports on the TCP host discovery list for each target IP address(target computer.) As with the prior ICMP ping test, multiple IPaddresses are advantageously tested in parallel (i.e., in batches) in apreferred embodiment. If a target computer responds with a TCP SYN ACK,then the target computer is added to the live list. Otherwise, the TCPSYN request to the target times out (i.e., a maximum time period passeswithout a response from the target computer).

In an alternative embodiment of the TCP scan test, a standard TCP fullconnect request initiated using the standard Window® Winsock interface.If the operating system confirms that a TCP three-way handshake has beencompleted, then the target computer is added to the live list. If thetarget responds with a TCP RST ACK, an ambiguous response, the targetcomputer is added to the “potentially live” list. Otherwise, the TCPrequest to the target times out.

The foregoing tests result in a list of live target computers (IPaddresses) on the live list. The target computers on the live list areremoved from the scan list. If there are any IP addresses that have notbeen confirmed on the “live list” or “potentially live list,” then athird step of scanning selected UDP ports on the target computer isperformed for IP addresses remaining on the scan list.

iii. Third Test (Intelligent UDP Port Scanning)

If any IP addresses (i.e., target computers) remain on the scan listafter the first two tests, then a third test of intelligent UDP portscanning is performed on the remaining addresses. As described below,intelligent UDP port scanning differs from traditional scanning of UDPports, which is notoriously inaccurate. When scanning TCP ports, aresponse from the target computer signals that the target port on thetarget computer is open. In contrast, while scanning UDP ports, noresponse from the target computer signals that the target port is open,and a response (an ICMP error message) will only be sent if the UDP portscanned is closed. The traditional method of scanning UDP ports thusresults in a significant number of “false positives” where a UDP scanresults in no response (suggesting an open port), but the UDP portscanned is actually closed. This may happen, for example, when afirewall or router blocks the ICMP error message from returning from thetarget computer or when the ICMP error message is simply lost whilereturning from the target computer. Over thousands of tests, such errorsbecome likely.

Sometimes, in order to “force” a response from the target computer, anintruder may send a malformed packet to a target port. While this knowntechnique increases the likelihood that an open UDP port on the targetcomputer can be identified, this technique also substantially increasesthe likelihood that the malformed packet could damage the targetcomputer. Also, firewalls or routers may detect and filter out malformedpackets, and such packets can alert the target network of an attemptedsecurity breach.

The intelligent UDP port scanning test in accordance with thisembodiment of the present invention employs an efficient, less intrusiveand more accurate method for scanning UDP ports on a target computer. Aswith TCP scanning, a UDP host discovery list of commonly used UDP portsis created.

An example of an LOP discovery list is shown in Table 4.

TABLE 4 Sample UDP Host Discovery List Service Port DNS 53 DHCP 67 BootP69 NTP 123 NetBIOS 137 File/Printer Sharing RPC Pipes WINS Proxy SNMP161 IKE 500

Unlike the data in traditional UDP port detection packets, the datacontained within the UDP packets sent in accordance with the presentinvention are specifically designed to prompt a reply from the scannedhost (i.e., target computer) based on knowledge of a service typicallyassociated with the UDP port. If no information is available about theUDP port, standard data (for example, the data representing a simpleASCII character return or control character) are placed in a UDP packet.In one embodiment, an exemplary UDP data probe packet is designed tosolicit a response from a NetBIOS name service that typically runs onUDP protocol at port 137. An exemplary UDP data probe for UDP port 137is shown in Table 5. In this case, the probe is advantageously a NetBIOSnode status request, which typically results in a known response fromthe UDP port.

TABLE 5 Sample UDP Data Probe Service Port Data probe (hex) NetBIOS 137A2 48 00 00 00 01 00 00 00 00 00 00 20 43 4B 41 41 41 41 41 41 41 41 4141 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 00 00 2100 01 — — — —

Similar UDP data probe packets can be created for other UDP ports knownto be associated with certain services, based on publicly knowninformation in Internet Requests For Comment (RFCs), publishedspecifications on private standards, analysis and monitoring of trafficon known ports, or well-established reverse engineering techniques.Particular protocols and particular UDP ports are subject to substantialchange over time, due to changes in standards, technology, operatingsystem, and the like. Preferably, when a data probe from a knownprotocol is not available for a certain UDP port, standard UDP packetswith data representing at least one simple ASCII carriage return aresent.

As with TCP port scanning, multiple UDP ports can be advantageouslyscanned in parallel. Typically, the system sends a UDP data probe packetto a set of UDP ports on each target computer. The system waits until aUDP data reply is received from one or more target computers or untilthe packets sent have “timed out.” If an ICMP unreachable reply isreceived, the hosts added to the “potentially live” list. Only thosetarget computer IP addresses not yet determined to correspond to live orpotentially live target computers alter employing ICMP, TCP and UDPscanning are left on the scan list.

The three-step discovery phase, employing ICMP, TCP and UDP scanningsteps, optionally is applied multiple times to increase the accuracy ofidentification of live target computers on the target network. In oneembodiment, after an initial pass through all three steps, if there areany remaining target computer IP addresses on the scan list that havenot been identified on the “live list” or on the “potentially livelist,” at least the ICMP and TCP steps are repeated a predeterminednumber of times for those remaining scan list target computers.Optionally, the UDP step may also be repeated. In particularly preferredembodiments, more intensive UDP scanning techniques, employing moreports, different data probe packets or more data packets, can be appliedto the target computers remaining on the scan list to provide a moredefinitive list of live target computers on the network. Alternatively,traditional UDP scanning with malformed packets can be attempted.

One obstacle to the usefulness of UDP scanning is that some targetcomputers will limit the number of ICMP responses sent within apredetermined “response latency” time period, ranging from about 250milliseconds to about one second. Thus, if a target computer is senttwenty UDP requests to various ports in one response latency period, itmay only send one or two ICMP error responses indicating that the portsare closed, even if all twenty ports tested are closed. This results insubstantial ambiguity as to UDP port status. In particular, whenapplying traditional UDP scanning techniques, many “false positives”(i.e., falsely reported open ports) are possible.

The present invention advantageously overcomes the foregoing problem by(1) determining dynamically the latency period of the target computer,and (2) continuing the UDP port scanning of each target port for atleast one entire latency period (or until an ICMP error response or UDPdata response is received) to ensure that a non-responsive UDP port isactually open and is not simply masked by the response latency. Thelatency period is determined by selecting a UDP port, preferably onethat is known to be closed, and sending UDP datagram requests for apredetermined maximum response latency period (i.e., for a time at leastas great as the target computer dead time period (approximately twoseconds in particular embodiments)). The time between responsive ICMPerror messages or the time between UDP response packets represents thestandard latency period. This test can be repeated to confirm thelatency period (dead time).

Once the latency period is determined, response validity is ensured bysending UDP requests continuously to the target port for at least thepre-determined latency time or until an ICMP error response or UDP dataresponse is received. If an ICMP error response is received, the portassociated with the prompting UDP request may be assumed to be closed.If a UDP data response is received, the associated port may be assumedto be open. If no response is received for the entire latency period,the associated port may be assumed to be open unless a router, firewallor packet loss has interfered with UDP port response.

The foregoing three-step discovery phase and optional intensive UDPscanning step are illustrated by the process flowchart in FIG. 6. Asdiscussed above and as illustrated in FIG. 6, the discovery phase beginswith a scan list 610, which is advantageously parsed into batches of IPaddresses 612. In a step 620, a batch of IP addresses is obtained forprocessing. In a step 630, the ICMP ping test is performed as discussedabove. Depending on the outcome of the test, each IP address is added toa live list 632 or remains in the present batch of IP addresses 612. Asillustrated, the process also operates with a potentially live list 634and a dead list 636.

After performing the ICMP ping test, the process determines, in adecision step 638, whether any of the IP addresses in the current batchhave not been added to the live list. If no IP addresses remain, theprocess proceeds to a decision step 640 where the process determineswhether all batches of IP addresses have been scanned. If batches of IPaddresses remain, the process returns to the step 620 and obtains a newbatch of IP addresses. Otherwise, the process ends.

If, in the decision step 638, the process determines that one or more IPaddresses have not been added to the live list, the process proceeds toa step 650 where the TCP discovery scan described above is performedusing a TCP discovery port list 652. IP addresses are added to the livelist 632 or to the potentially live list 634 in accordance with theresults of the scan. Then, in a decision step 654, the processdetermines whether any of the IP addresses in the current batch has notbeen added to the live list or the potentially live list. If no IPaddresses remain, the process proceeds to the decision step 640discussed above.

If, in the decision step 654, the process determines that one or more IPaddresses have not been added to the live list or the potentially livelist, the process proceeds to a step 660 where the intelligent UDPdiscovery scan described above is performed using a UDP discovery portlist 662. IP addresses are added to the live list 632, the potentiallylive list 634 or the dead list 636 in accordance with the results of thescan. Then, in a decision step 664, the process determines whether anyof the IP addresses of the current batch have not been added to the livelist, the potentially live list or the dead list. If no IP addressesremain, the process proceeds to the decision step 640 discussed above.

If, in the decision step 662, the process determines that one or more IPaddresses have not been added to the live list, the potentially livelist or the dead list, the process proceeds to a step 670 where theintensive UDP discovery scan described above is performed using a secondUDP port list 672, which advantageously includes additional ports toscan. In one embodiment, the second UDP port list 672 is the UDP serviceport list advantageously described below, but any combination of UDPports may be used IP addresses are again added to the live list 632, thepotentially live list 634 and the dead list 636 in accordance with theresults of the intensive scan. Then, in a decision step 674, the processdetermines whether the discovery testing needs to be repeated. If all IPaddresses have been added to one of the three lists and no IP addressesremain, the process proceeds to the decision step 640 discussed above.If any remaining IP addresses remain that have not been added to one ofthe lists, then the process determines whether the scanning steps havebeen performed a predetermined number of times for the current batch ofIP addresses. If the steps have been performed a predetermined number oftimes, the process proceeds to the decision step 640. Otherwise, theprocess returns to the ICMP ping test 630 to again process the remainingIP addresses.

As discussed above, the intensive UDP discovery scan 670 is optional. Ifthe intensive UDP discovery scan 670 is not included, then the decisionstep 664 following the intelligent UDP discover scan 660 advantageouslyincludes the additional decision of whether to repeat the scanningprocess based on whether the scanning process has been performed apredetermined number of times.

B. Service Discovery

In one embodiment, the present invention then proceeds to examine eachhost (i.e., target computer) in more detail using the live list andoptionally using the potentially live list as well. In servicediscovery, a set of common TCP service ports and a set of common UDPservice ports are scanned. The TCP service discovery list and the UDPservice discovery list are typically substantially larger than the TCPhost discovery list and the UDP host discovery list. Each list typicallyincludes some subset of ports that are commonly used for communications.For example, each list may include anywhere from a few to hundreds ofports. Typically, each list includes ports such as those shown in Table6 (an exemplary list of default ports publicly reported by Microsoft®for Windows® 2000.) This list is not exhaustive, and changes intechnology, protocols, network infrastructure and operating systemsfrequently change port requirements.

TABLE 6 Example Set of UDP and TCP ports for Service Discovery ServiceUDP Ports TCP Ports NetBIOS 138, 137 Client/Server 135 CIFS 445 139, 445DCOM 135 135 DHCP 67, 68, 135 DNS 53  53, 139 Exchange 5.0 135 IMAP 143,993 LDAP 389, 636 POP3 110, 995 RPC 135, 1500, 2500 SMTP 25 NNTP 119,563 File Sharing 137 139 FTP 20, 21 HTTP 80, 443, 8000, 8080 IIS 80 IKE500 IRC 531 ISPMOD 1234 Kerberos  88, 464 88, 464, 543, 544, 2053 WinNTLogin 137, 138 139 Macintosh File Services 548 MSN Chat/Messaging 1801,3527 135, 569, 1801, 2101, 2103, 2105, 6665, 6667 NetMeeting 389, 522,1503, 1720, 1731, PPTP 1723 Printer Sharing 137 139 SNTP 162SQL/Pipes/RPC 137 139, 1024-5000, 1433 Telnet/Terminal  23, 3389 UNIXPrinting 515 WINS 137 42, 102, 135, 137

Because there are 2¹⁶ (65,536) possible ports on each target computer,the selection of a subset of ports is preferred because time constraintsgenerally preclude scanning of all ports on each target computer,especially on a large network. Similarly, random selection of ports oneach target computer is unlikely to be fruitful because an averagetarget computer will run less than a dozen, and in rare cases dozens orhundreds, of services, making the probability of hitting an open portthrough random selection of a port inefficient and inaccurate.

In accordance with preferred embodiments of the present invention, TCPservice discovery uses the large list of TCP service scan polls, a fewof which are shown above, and attempts to connect to each target port oneach-target computer. As with Host Discovery, described above, standardTCP SYN scanning requires waiting for a SYN ACK response from eachtarget port, or TCP “full connect” scanning requires waiting for anoperating system message indicating that a three-way handshake betweenthe target computer and scanning system has been completed. Targetcomputers that respond positively to either of these attacks are addedto a list of vulnerable computers to undergo vulnerability assessmentfor each open target port found.

In accordance with preferred embodiments of the present invention, UDPservice discovery uses the large list of IMP service scan ports, a fewof which are shown above, and attempts to connect to each target port oneach target computer. As with Host Discovery, described above, thepresent invention may advantageously use the improved UDP data probepackets for any port recognized to be commonly associated with aparticular service. Alternatively, packets that include datarepresenting standard characters, such as one or more ASCII characterreturns, may be used. Target computers that respond positively to thisattack are added to a list of vulnerable computers to undergovulnerability assessment for each open target port found. Thevulnerabilities used are typically limited to those associated with theoperating system of the target computer as discovered by the operatingsystem identification system described previously, and by thosevulnerabilities associated with the open ports found on the targetcomputer. If the operating system of the target computer cannot beconclusively identified, then typically all vulnerabilities associatedwith the open ports found on the target computer during the servicediscovery system described herein are tested against the targetcomputer.

As with Host Discovery, a more intensive UDP scanning regime can beapplied to target computers that do not respond to a simple UDP dataprobe packet. The more intensive UDP scanning regime advantageouslyuses, for example, traditional UDP port scanning in combination with theoptional latency time resolution described above.

After vulnerability assessment, an optional active assessment of targetcomputers takes place. Active assessment applies knowledge of targetcomputer operating system, open ports, as well as information recoveredfrom the target network during vulnerability assessment, to further testknown vulnerabilities against each target computer.

Parallel Processing of Multiple Ports

In one preferred embodiment, the present invention advantageouslyperforms port scanning in “batches,” rather than completing serialscanning of individual ports, one after another. This allows smallpieces of a large scan to be completed and saved to a database, notrequiring the entire results of a large scan to be held in memory all atonce. For example, if a class A network is tested, hundreds of millionsof ports need to be scanned merely for host discovery. The system may beadvantageously adapted to technical limitations in older networkequipment to scan ports of computers in a very large target network withmultiple, significant IP address ranges. In the event of network orsystem failure, the system resumes particularly large scans followingthe last known successfully completed batch.

During a port scanning process, preferred embodiments of the presentinvention identify small portions or “batches” of the entire scan rangeof IP addresses, comprising, for example, 64 target computersrepresented in the scan range. Host discovery begins using a first batchof target computers. When all live hosts in the first batch have beendiscovered, service discovery of TCP and UDP services is performed onthe live hosts in the first batch, along with other testing servicessuch as operating system identification, tracerouting of networktopology, and active assessment of vulnerabilities, described herein.When a batch is completed, the results are stored in a vulnerabilitydatabase. Then, the next batch of 64 target computers are similarlyprocessed, and so on, until the entire scan list has been processed forthe target network.

Preferably, a large number of target computers are tested on one or asmall number of ports in parallel, rather than a large number of portsbeing tested on a single or small number of target computer in parallel.Typically the former method prevents undue load on any single targetcomputer, prevents network overload, and reduces the risk of triggeringtarget network security alerts. Occasionally, the later method may bepreferred if, for example, a few target computers are selectivelysingled out for scanning.

More particularly, in one exemplary embodiment, the present inventionsimultaneously uses a set of 640 packet slots. A pocket slot is anadvantageously allocated space in memory that keeps track of a sentpacket while waiting for a response or for the packet sent to time-out.Thus, when processing a batch of target computers, up to 640 ICMPrequest packets can be handled simultaneously, but it will beappreciated that a different number of slots, more or less than 640, maybe allocated and used simultaneously. When an ICMP response is receivedfor one of the packets sent, or after the packet has timed-out, the slotallocated for the packet is then reallocated to send a new packet andmonitor any response or time-out. Thus, packets can be kept moving at arapid rate since there is a small average delay between sending of onepacket and receipt of a response and/or time out for another packet. Itis more than likely, for example, that by the time the 640^(th) ICMPrequest packet has been sent, a response to one of the sent packets willhave been received, thereby freeing the associated slot for handling ofanother packet. A similar methodology applies to the handling of TCP SYNpackets, UDP host discovery, and service discovery in general. As thoseof ordinary skill in the art will appreciate, operating systemidentification and tracerouting can use similar batched parallel portmonitoring. For those processes, the number of slots used is not limitedto 640 slots, and can be varied for programming or scanning efficiency.

As an example, one embodiment of the present invention uses a batch sizeof one hundred target computers for simultaneous scanning. For hostdiscovery, the ICMP scanning process sends 100 ICMP echo requests andmonitors responses and time-outs. Because this is less than thisembodiment's 640 packet slots, all ICMP request packets can be sent out,and responses or time-outs for all packets can be monitored at the sametime. Assuming a TCP host discovery list of 10 TCP ports, the TCP hostdiscovery scanner will ultimately send out 1000 packets (100 targetcomputers×10 ports=1000 packets) to probe all listed ports of all listedcomputers. In this embodiment, the scanner will initially send out 640packets in a sequential burst using all 640 packet slots. However, asdiscussed above, by the time the 640^(th) packet is sent, it is probable(depending on time-out settings and how many responses the systemreceives) that at least one of the 640 packets sent earlier will havegenerated a response or a time-out, freeing that packet slot for sendingone of the remaining 360 packets. By constantly monitoring the receiptof response packets and time-outs, the entire list of target computerscan be tested with little wasted time.

Larger batch sizes and more packet slots can be used, but the efficiencyof such use depends on how much of the target network comprises livehosts, time-out values, network response time, memory and other systemresources, and the like. In general, very large batch sizes takecorrespondingly longer in the host discovery phase, such that by thetime the system begins scanning the discovered hosts in the servicescanning phase there is a greater possibility that those targetcomputers may have changed in some way.

The above-described service discovery phase is illustrated by theprocess flowchart in FIG. 7. The process starts with a live list 710,which advantageously corresponds to the live list 632 generated by thehost discovery process illustrated in FIG. 6. The process may alsoinclude the potentially live list 634 generated in FIG. 6; however, forease of explanation, the potentially live list is not shown in FIG. 7.The IP addresses in the live list 710 are advantageously parsed intobatches of IP addresses 712. As described below, the process of FIG. 7operates on a target computer vulnerability database 714 and a knownvulnerability database 716.

In a first decision step 720 in FIG. 7, the process determines whetherTCP SYN scanning or TCP “full connect” scanning is being performed. Asdiscussed above, the TCP full connect scanning process requires theprocess to wait for an operating system message indicating that athree-way handshake between the target computer and the scanning systemhas been established. In the TCP SYN scanning process, the process,waits for a SYN ACK response from each target port, in which case, thetarget computers can be processed in parallel, as discussed above. Inboth cases, the process proceeds to a step 722 to obtain a first batchof EP addresses representing a first batch of live (or potentially live)target computers. If TCP full connect scanning is being performed, theprocess operates on a smaller number of ports on the target computers atone time. The process then proceeds to a decision step 730.

In the decision step 730, the process determines whether all the livetarget computers have been processed in TCP full connect scanning orwhether all the batches of live target computers have been processed inTCP SYN scanning. If all the target computers or all the batches oftarget computers have been processed, the process ends. Otherwise, theprocess proceeds to a TCP service scan routine 740 wherein the processuses a TCP service discovery list 742 to identify the TCP service portsto be examined for each target computer. As described above, TCP packetsare sent to the identified TCP service ports of each target computer,and the target computer vulnerability database 714 is updated for eachtarget computer in accordance with whether a response is received or isnot received from each target computer for each TCP service port scannedand using the known vulnerability database to obtain the vulnerabilityinformation for the particular TCP service ports that are determined tobe open.

After performing the TCP service scan routine 740, the process proceedsto an optional UDP latency test 750 wherein the latency of each targetcomputer is determined and stored in a latency database 752. The processproceeds from the latency test 750 or directly from the TCP service scanroutine 740 to a UDP service scan 760 wherein the process uses a UDPservice discovery list 762 to identify the UDP service ports to beexamined for each target computer. As described above, UDP packets aresent to the identified UDP service ports of each target computer, andthe target computer vulnerability database 714 is updated for eachtarget computer in accordance with whether a response is received or isnot received from each target computer for each UDP service port scannedand using the known vulnerability database to obtain the vulnerabilityinformation for the particular UDP service ports that are determined tobe open.

After completing the UDP service scan routine 760, the process proceedsto a decision step 770 wherein the process determines whether a responsehas been received from all the scanned service ports. If not, theprocess determines whether the scanning of the current target computeror batch of target computers has been performed a predetermined numberof times. If all the scanned service ports have responded or if thescanning has been performed a predetermined number of times, the processreturn's to the step 720. Otherwise, the process returns to the TCPservice scan routine 740 to scan the service ports that have notresponded.

C. Banner Grabbing

“Banner grabbing” is a method of stripping relevant information frompackets received from a target computer. In one embodiment, for eachtarget computer in the live list, an attempt is made to perform bannergrabbing against each open TCP port and each open UDP port discoveredduring the service scan phase. If information is successfully obtainedfrom a responsive TCP or UDP packet, this information is stored in adatabase in association with the target computer from which theinformation is obtained. The stored information is subsequently used tocollect vulnerability information on the target computer, and thevulnerability information is also stored in a database.

For each open TCP port located during the service discovery phase, a TCPdata probe is sent to that port if the port is known to be typicallyassociated with a particular service. Thus, for example, when sending aTCP data probe to a target TCP port 80 on a target computer, where TCPport 80 is well known as the common service port for HTTP, the systemsends an HTTP-compliant GET request, and strips useful information fromany TCP response packet sent back from the target computer. As noted inthe above tables, similar commands can be used for other ports with wellknown services running thereon. The useful information obtained mayadvantageously be transformed or translated into a readable orprocessable form (e.g., text) and stored for later reporting.

For each UDP port discovered during the service discovery phase, asimilar UDP data probe is sent to each UDP port on the target computerknown to be typically associated with a service. Thus, for example, fromthe foregoing tables, UDP port 137 is known to be associated with aNetBIOS service. In one embodiment, the system sends a NetBIOS NodeStatus Command, for example, and strips and stores useful informationfrom any response packet sent by the target computer. Again, theinformation obtained in this manner may advantageously be transformed ortranslated into a readable or processable form (e.g., text) and storedfor later reporting.

IV. Tracerouting

In one embodiment, for each target computer in the live list, an attemptis made to perform an ICMP traceroute between the system and the targetcomputer. If the ICMP traceroute is incomplete, an attempt is made toperform a TCP traceroute between the system and the target computer.Based on the traceroute results for each target computer, a map of thetarget network topology is created and stored in a database.

Initially, traditional ICMP tracerouting is performed. A number ofpackets are sent to the target computer with varying TTL (time to live)values in the TCP/IP header, starting with a TTL of 1. If the ICMP echorequest packet fails to reach the destination target computer, it willreturn an ICMP destination unreachable packet containing the IP addressof the router/host that the packet was returned from. Packets thatarrive at the target computer itself return an ICMP echo reply packet.Based on the known TTL value, the number of “hops” between the systemand the target computer, and the router/host at each “hop” can be mappedout. When all packets have arrived or timed out, if there is arouter/host and IP address associated with each “hop” between the systemand the target computer, the traceroute step is completed for thattarget computer. The ICMP traceroute is continued for a number ofpredetermined passes until a complete trace is received or the maximumnumber of passes is completed. If, after the pre-determined number ofpasses the tracerouting of the target computer is incomplete, then a TCPtraceroute is attempted.

TCP tracerouting works similarly to ICMP tracerouting, except TCP SYNpackets are used. In some instances, TCP packets are more reliable atcompleting otherwise incomplete traces, because, for example, ICMPpackets are sometimes blocked by firewalls or routers. Typically, theTCP port chosen is taken from the list of open ports discovered for thetarget computer that is the subject of the traceroute. As with ICMPtracerouting, the TTL value in each SYN packet is incrementallyincreased, and the return of ICMP unreachable packets and SYN ACKpackets is monitored for all “hops” between the scanning system and thetarget host. Through the combination of ICMP tracerouting and TCPtracerouting, a complete map to each target computer, and collectively arelatively complete map of the target network topology, isadvantageously created.

The network maps are an attempt to represent in the most concise waypossible the topology of the network as discovered by traceroutingmethods. Basically, packets are sent to each discovered host in thescanned network with the Time-To-Live field set to the hopcount at whicha packet indicating failure to transmit due to that hopcount will besent by the machine that is that many hops away from the scanningmachine. By increasing the TTL and storing the IPs of the machines thatrespond until getting a response from the host in question, a string ofIPs is built up that represents the machines that led up to that host.The procedure is far from perfect. A machine at a given hop may notrespond within the time expected by the tracerouting algorithm, or itmay not respond at all if it is a firewall that blocks the traceroutepackets. Any approach that can exist must deal with this uncertainty insome way. In one embodiment, any unknowns are assumed to be firewalls.

The algorithm typically employed is presented with a set of discoveredhosts and each host includes a IP address that represent what thetracerouting algorithm initially determines are the machines leading upto them. This string may include unknowns which are denoted by0xFFFFFFFF or 255.255255.255. The algorithm operates as follows:

-   -   CONDENSE UNKNOWNS: Condense consecutive unknowns into a single        hop with unknown IP address (0xFFFFFFFF). If a traceroute is        performed to a given hop and an unknown is received, it is        probable that every hop after that will also be unknown because        the first unknown bop is a firewall blocking the packets.    -   UNKNOWN RESOLUTION: Attempt to resolve unknowns by looking        through the other routes to see if a route exists with the IP        addresses on either side of the unknown in this route that are        connected by all known machines. If found, replace the unknown        with those machines. This attempts to eliminate spurious        unknowns so they are not mislabeled as firewalls. It will not        eliminate actual firewalls as they will typically be unknown.    -   BUILD SET OF NODES: Build up a list of structures (structs) of        type ROUTENODE. This is a list in which the IP addresses are        guaranteed unique (except for unknowns as detailed later) and        represents the set of all IP addresses discovered in the network        (i.e., the hosts discovered by the scanning process and the hops        leading up to them discovered as by the tracerouting process.)        The m_pHost member of each ROUTENODE struct will be NULL if the        IP address is not one of the hosts discovered in the scanning        process and will point to the host data discovered by that        process otherwise. As mentioned, the known machines are unique        by IP address. The unknowns are further qualified by the IP        address immediately preceding them. As a result, unknowns with        the same IP address preceding them are typically considered to        be the same firewall and are therefore represented by a single        ROUTENODE in the list.    -   FELL IN CONNECTIONS: Each ROUTENODE struct has a list of        ROUTENODE pointers in it which represent the machines that        ROUTENODE is directly connected to. The algorithm next fills        this in to guarantee that the IP addresses are unique in each        list of connections. Note that these pointers point to other        ROUTENODE structs in the list (i.e., the list is typically a        self contained bunch of data.)    -   COMPUTE DISTANCE FROM INTERNET: The traceroute information is        once again traversed for each host and for each IP address. The        corresponding ROUTENODE struct is looked up in the list and the        struct's m_nDistFromInternet is set according to the hopcount in        the route. This is typically done to represent a maximum        hopcount. In other words, the m_nDistFromInternet fields are        initialized to 0, and then, if the hopcount in a traceroute IP        string is greater, the m_nDistFromInternet is set to that        hopcount. For example, an IP address (let it be called “d,” for        example) may appear in one route as a-b-d and in some other        route as a-b-c-d, where “a,” “b,” and “c” are other IP addresses        on the route to the IP address c. When this part of the        algorithm completes, d will have m_nDistFromInternet=4. This        information is used by the algorithm to know if one machine        precedes another. Note that this maximum of discovered hop        lengths is a heuristic for the sake of making the problem        reasonably computable. It could go awry if a particular machine        should be drawn as connected to another machine (because it is        directly connected to it) and precedes it in one route, but it        is not drawn that way because the machine is in some other route        that bumps its m_nDistFromInternet to the same or more than that        of the machine it is connected to in the other route. This        situation is rare, and this heuristic is typically acceptable.    -   BUILD ROUTER LIST: The algorithm then traverses the ROUTENODE        list in order to build up a list of ROUTER structs. A ROUTER        struct contains a pointer to a ROUTENODE believed to be a ROUTER        and a list of ROUTENODE pointers that are leaf (end of route)        machines it is connected to. A leaf is any ROUTENODE that is        directly connected to only one machine (besides itself.) For the        purposes of this algorithm, a ROUTER is that machine. This stage        of the algorithm builds up a list of ROUTER structs, and, within        each ROUTER, builds a list of leaf ROUTENODEs connected to that        ROUTER. The algorithm also marks a Boolean field within the        ROUTENODEs that are being designated ROUTERS as it will become        necessary to know which machines in the ROUTENODE list are        routers without wanting to consult the ROUTER list.

Next the refinements to the algorithm are discussed, but first it isuseful to discuss how the map would be drawn if the algorithm finishedhere. At this point, the algorithm has a set of ROUTERs, and within eachof those, has the set of leaves connected to that ROUTER. Prior to therefinements about to be detailed, the map renderer would draw eachROUTER as a sphere and all of its leaves as small spheres embedded in aring in orbit around the ROUTER sphere. The algorithm would then lookfor other ROUTERs whose m_nDistFromInternet fields are less than thisROUTER's m_nDistFromInternet (i.e., look for a ROUTER that is directlyconnected to this ROUTER and precedes it.) The algorithm takes thegreatest m_nDistFromInternet router that it finds and connects thisROUTER to it visually. If it finds no preceding ROUTERs, it connectsthis ROUTER to the internet cloud in the center of the map. The refinedalgorithm still does all that is described above, but typically notbefore doing a bit more processing.

-   -   ROUTER PROMOTION: There are circumstances when the algorithm as        it has been detailed thus far would produce a map in which a        ROUTER has leaf nodes surrounding it all of which have the same        subnet, for example they might all be 149.17.1.xxx. The first 1,        2, or 3 digits (8 bits each) will be the same. That ROUTER has a        ROUTER of less m_nDistFromInternet directly connected to it that        has exactly 1 leaf node and that leaf node has the same IP        address digits in common as all the ones in the first ROUTER's        leaf list. In this case, although the traceroute data suggests        that the first ROUTER and that single leaf are different        machines, they are likely two NICs (Network Interface Cards) on        the same machine. Hence, the algorithm “promotes” that ROUTENODE        by adding its IP address to the m_lnOtherNics member of the        first ROUTER's ROUTENODE and then removing it from the other        ROUTER's list of leaves and marking that ROUTER's ROUTENODE to        be no longer a ROUTER. That ROUTER is also removed from the        ROUTER list. On the map then, the ROUTER's primary IP address is        represented as usual but now there is a grey bar and the other        IP address underneath it. The algorithm supports doing        multi-homed ROUTERS and will represent all the IPs that get        promoted. The multi-homed case is easily imagined by extending        the dual-homed example discussed here.    -   OTHER TYPE OF ROUTER PROMOTION: The preferred algorithm performs        another type of router promotion as well. If exactly one leaf        around some ROUTER fulfills a heuristic, it will be promoted to        another NIC on the ROUTER. In order to test for the heuristic,        the machine needs to be a host discovered during the scanning        process because that is where the information comes from. It is        noteworthy that most leaves will be discovered hosts. Although        the algorithm does not demand this, and traceroute information        may produce non-discovered-host hops that only have one thing        connected to them and thereby make leaves out of them, since        tracerouting is being done to the discovered hosts, the leaves        will tend to be discovered hosts. The heuristic is, in one        embodiment, as follows: if TCP 2001, 4001, 6001, or 9001 is        discovered, or if UDP 520, or both UDP 23 and 79 are discovered,        or if the discovered operating system is Cisco, that ROUTENODE        is assumed to be a router-IP address and it is promoted (IP        address added to the ROUTER's m_lnOtherNics and ROUTENODE        pointer removed from its leaves).    -   FIREWALL PROMOTION: Firewall promotion is similar to the router        promotion heuristic detailed above. In one embodiment, if        exactly one leaf around a firewall satisfies the heuristic then        it gets promoted into the firewall's other-NIC list resulting in        the map printing “Firewall,” but now the known IP address is        underneath it separated by the gray bar. The heuristic, in one        embodiment, is if TCP 256, 257, 264, 265 is found on a machine        then it is assumed to be a firewall.    -   NUMBER FIREWALLS: This is the last step of the algorithm. The        firewalls are sorted in order of the IP address that precedes        them and are then numbered so that the map can print        “Firewall-1, Firewall-2, . . . , etc.” on the report.

In this manner, an entire network map can be relatively accuratelystored internally, and translated into a visual representation forreporting.

V. Vulnerability Identification and Active Assessment

For each known TCP port, UDP port, and operating system, the knownvulnerabilities for that configuration are stored in a vulnerabilitydatabase based on vulnerability identification codes. Advantageously,for many vulnerabilities in the vulnerability identification database, amethodology for testing the vulnerability can be written into anautomatic script, which will assess the actual weakness of the targetsystem to the suspected vulnerability. In one embodiment, these scriptsare prepared in a assessment security scripting language, and arepreferably prepared in FASL. FASL is a scripting language based on C++and Java implementation, in one embodiment. FASL provides an adjustable,automated language for security testing various vulnerabilities.Multiple FASL scripts advantageously may be run in parallel. Forexample, in one embodiment up to eight simultaneous scripts may be run.Each FASL script, for example, will respond with a success or failureresult noting whether the target computer was vulnerable or not to thegiven vulnerability identification code. The information collected bythe FASL script from the target computer, and the success or failure ofthe attempt, are stored in a database related to the target computer forlater reporting, for use in additional vulnerability testing, or forrepeating additional testing.

VI. FASL Scripting Language

The implementation of the FASL language is similar in construction toC++. In one embodiment, FASL includes member functions in structureobjects, constructors and destructors in structure objects, inheritancein structure objects, arrays of scalar types, new scalar type “binary”and associated functions, string constants that support embedded hexcodes including embedded zero bytes, RPCCheck( ) and SMBCheck( )functions for RPC and Netbios checks, debugMessage( ) on all scalartypes that produces hex output on binary type, recursion, functionoverloading, reference parameters, and support for Active-Assessment.

In one particular implementation of FASL, all variables are stackvariables. In addition to permitting recursion, this also allows a parsetree to be built once and then used to execute the same script bymultiple threads. The execution architecture in FASL treats the parsetree as a read-only data structure. Hence, other than considerationssuch as two instances of the same script attempting to instantiate aSocket on the same target computer IP and port (which should not happenin practice), FASL is completely thread-safe.

A. Scalar Data Types

Scalar data types are those native types in the language that take upone slot on the execution stack. Basically, any variable that can bedeclared is a scalar type, an army of a scalar type, or an instance of astructure. The scalar types are as follows:

TABLE 7 FASL Data Types Scalar Type Definition void Function return typeint 64 bit signed integer string String of printable characters ofarbitrary length, terminated by a null Binary String of arbitrary bytesof arbitrary length, terminated by a null. Type keeps track of itslength Char 8 bit signed integer (interchangeable with int) Boolean Trueor false (not interchangeable with int)

Typically, a string is NULL terminated. This means that internally thestring is represented as a string of characters with a zero marking theend. This zero's existence is always implicit, however. In other words,there is no string function that will return you the zero. The length ofthe string is computed by counting the number of characters up to butnot including the zero. This also makes it so that if a constant isassigned to a string of, for example, “this is a string\x0 with stuffbeyond the zero.” the value of that string will be “this is a siring”and its length will be 16. Type binary typically does not use a zero orany other delimiting character in its internal representation. Thestring constant example with the embedded zero would have everythingafter the zero also in the binary.

For example,

binary b = “1234”; // length = 4. string s = “1234”; // length = 4.binary b = “zzzz\x0ssss”; // value = “zzzz\x0ssss”, length = 9. string s= “zzzz\x0ssss”; // value = “zzzz”, length = 4.

Types which are equivalent to int (interchangeable in expressions withint) are as follows:

TABLE 8 Additional int-like FASL types Type Description Attackspecifying type of attack Operatingsystem specifying target OS of ascript Protocol specifying protocol used by a Socket Returnvaluespecifying status of script (script return value) Ipservice IP type ofservice Ipoptions IP options Ipoffset IP offset

Keywords that indicate a constant value of a given type are as follows:

TABLE 9 Additional FASL Constants Constant Keyword Value null 0 (int,char, boolean) true 1 (boolean) false 0 (boolean)

The types above that are equivalent to int also have keywords indicatingconstant values of those types. They are (respective to above) asfollows, for example:

TABLE 10 FASL Type Constants Type Constants attack ATTACK_UNKNOWN,ATTACK_INTRUSIVE, ATTACK_DOS, ATTACK_NONINTRUSIVE operatingsystemOS_UNIX, OS_MAC, OS_WINDOWS, OS_UNKNOWN, OS_ROUTER protocol TCP, UDP,ICMP, IGMP retumvalue RETURN_SUCCESS, RETURN_FAILURE, RETURN_TIMEOUTipservice LOWDELAY, THROUGHPUT, RELIABILITY, MINCOST, CONEXP, ECTCAPipoptions EOL, NOP, RR, TS, SECURITY, LSRR, SATID, SSRR, RA ipoffsetRESERVED, DONT, MORE

B. Statements

A FASL script is typically a list of statements. These statements aregenerally separated by semicolons. The exception to this rule is thatstatements that involve blocks (other statement lists enclosed by {and})do not typically require semicolons to separate them. A semicolonconstitutes a valid (empty) statement so it does not hurt anything toput semicolons after statements involving blocks but it accomplishesnothing. A new block represents a new scope. Any variables declared inthat scope will be accessible only in that scope, and if they havedestructors, those destructors will be called at the end of the scope.Variables can be declared with the same name as variables in scopes thatenclose the scope in which they are declared. They will override thevariables in the outer scopes which are otherwise accessible to theenclosed scope. Variables of the same name as other variables in thesame scope will generate an error however. A statement can be one of thefollowing, each of which will be detailed further below:

-   -   Function declaration: A named list of statements with parameters        that appear to the list of statements as declared variables in        their scope but whose values are copied from expressions or else        refer to variables supplied by a function-call which is a type        of expression. Function declarations may only occur in the        topmost scope of the script.    -   Structure declaration: A declaration of an entity which can have        both data members and member functions. The member functions all        have an implicit first parameter which is a reference to the        object instance upon which the function is being called.    -   Variable declaration: A declaration of a variable which then        exists in the scope in which it was declared. Variables can be        simply declared or as part of their declaration they can be        initialized by assigning them to an expression or constructed by        supplying constructor parameters in parenthesis after the        variable. Note that scalar types have no constructors. On types        that do have constructors, the parameter list must match a        constructor that exists for that type.    -   Expression; This can be a function call, a constant value, a        variable, a member selection (which is either a member variable        or member function), and arithmetic and logical operations on        variables, constants, etc.    -   While loop: This is a control structure that has a        block/statementlist/scope that is executed for as long as a        given condition (expression) resolves to true.    -   Repeat loop: This is a control structure that executes its block        a given integer amount of times that an expression resolves to.    -   If statement: This is a control structure that executes a block        upon an expression evaluating to true and executes an optional        else block if it is false.    -   For loop: This control structure has 3 lists of expressions        separated by semicolons enclosed in parentheses. Within the        lists (which can be empty, have one expression, or more than        one) if there are more than one expression, they are separated        by commas. The first list is executed initially. The next is a        condition that must be true for the block to execute (in a list        of expressions all must be true), and the last is the iterator        list of expressions that gets executed each time through the        loop.    -   Block: Note that many statements own blocks. A block may also        exist on its own without being owned by a control statement or        function declaration. An unowned block may be coded in        circumstances when construction and destruction of something        needs to happen at a given point that cannot be accomplished in        any of the “normal” scopes.

C. Function Declarations

Functions are declared using the “function” keyword. They are declaredas follows:

function [<scalar-return-type] <functionname>(<argument-list>) { <body>}

When a return type is not specified, int is implicitly assumed. Theargument-list can be empty (i.e., “function <functionname>( ) . . . ”.)Every script typically needs a “function faslmain( )” and will error ifone is not found. The function faslmain( ) can be explicitly called fromanywhere in the script but if no call to faslmain( ) is found in thetopmost scope, a can is implicitly inserted at the end of the script.Functions may be overloaded, such that multiple functions with the samefunctionname can exist provided their argument-lists are different. Theargument-list has the form “<argument>, <argument>, . . . , <argument>”.An argument can be the following forms:

-   -   Pass by copy. <scalar-type> <distinct-variable-name>: Anything        the function does to this variable is not reflected in the        corresponding expression supplied in the call. The expression        can be constant.    -   Pass by reference. <scalar-type>&<distinct-variable-name>:        Anything the function does to this variable is reflected in the        corresponding variable supplied in the call. The call must        supply an expression that reduces to a variable corresponding to        this argument (i.e., only variables or structure member        selections that reduce to variables.)

The (possibly empty) <body> consists of a list of statements. If astatement which is “return <expression>” is encountered anywhere in thisbody, the execution of the function ceases at that point and control isreturned to the caller of the function with the value returned being thevalue that function presents to the expression in which it participates.Functions can be called without using the value they return as well.

For example,

---------------------- function faslmain( ) { int x; x = 5; } functionstring DoStringStuff(int x) { return intToString(x); } function voidDoStringThing(string& s) { s = “the string”; // DoStringThing(szThing)will set // szThing to “the string” } ---------------

Variable Declarations

Variable declarations are declared as follows:

-   -   <typename> <var>[, <var> . . . ];

In the case of structures, <typename> is typically expressed as“structure <structurename>” or, alternatively, a structure variable oftype “OBJECT” can be declared as “OBJECT o;”.

A <var> is one of the following:

-   -   <identifier>: This is a simple declaration. If <typename> is a        structure and the default (no arguments) constructor exists, it        is called.    -   <identifier>=<initializer expression>: The expression is        evaluated and the result assigned to the variable at declaration        time. Note that the type returned by the expression must be        compatible with <typename>.    -   <identifier>(<params>): <params> is a comma separated list of        expressions. The constructor matching that signature in        <typename> is called. Note that <typename> needs to be a        structure.    -   <identifier>[<array-dimension-expression>]: <typename> must        indicate a scalar (non-structure) type. The expression must        resolve to a constant integer (i.e., no variables or function        calls in it). This declares <identifier> to be an array variable        of given dimension of <typename>.    -   For example,

------------ OBJECT o; structure OBJECT o; OBJECT o(5, 6, “something”);int x = 8, y, z[6 + 7]; -----------

D. Structure Declarations

Structures are declared using the “structure” keyword. They are declaredas follows:

structure <structurename> [extends <parentstructurename>] {<member-list> };

The parameter <member-lists> is a possibly empty list of <member>s. A<member> is typically either a function declaration or a variabledeclaration. The only syntactic difference between these things whenused in structure declarations versus not is that member variablescannot have initializer expressions or constructor parameters. Membervariables can be arrays however.

When “extends” is used, this structure “inherits” all the members of theparent. Any member functions in this structure that are the same nameand signature as one that is in the parent structure will override thatparent structure's function.

A “constructor” is a member function that gets called when a structurevariable is declared and a “destructor” is a member function that getscalled when a variable goes out of scope.

Any member function whose name is <structurename> is a constructor andcan have any or no parameters. There can be zero or one member functionwhose name is ˜<structurename> and has no parameters, and this is thedestructor. Some subtleties that are not immediately apparent are asfollows: If this structure extends an object that has constructorsand/or a destructor or has member variables that are structures thathave constructors and/or a destructor, then each constructor in thisobject will implicitly contain a call to the default constructor in theparent and/or owned object(s) and similarly the destructor for thisobject will have call(s) to destructors of parent/owned object(s).Further, if a parent or owned object has a constructor and/or destructorand this object does not, one will be created in this object for thepurpose of calling all the constructors/destructors of parent/ownedobjects. Constructors and destructors should be declared as “function<structurename> . . . ” or “function ˜<structurename> . . . ” (i.e., noreturn type.)

Usage of declared structure variables is accomplished with memberselection using the “.” character. For example:

------------ OBJECT o; o.m_intmember = 5; o.m_ownedstructuremember.m_x =8; o.DoSomething(5, 6, “stuff”); ------------

E. Expressions

Expressions are variables, function calls, constants, member-selections,and combinations of these things with operators serving as theconnectors. For the purposes of this discussion, expressions may bedefined recursively, such that, for example, <expression>+<expression>is an expression. In expressions involving operators (assignment,arithmetic, logical, etc.,) it is customary to refer to the expressionon the left as the “lvalue” and the expression on the right as the“rvalue.” In FASL as most languages, the lvalue and rvalue in anyexpression must return compatible types (usually the types must be thesame but sometimes, as with int and char in FASL, different types can becompatible). Additionally, some operators only work on some types. Thereis also the notion of operator precedence, meaning that in the absenceof overriding parentheses, some operators will be given precedence overothers. So for example, 3−5+7 will be evaluated left to right but 3−5*7will multiply 5 by 7 first and subtract the result from 3. A list of allthe operators in order of precedence follows:

Functions and Constants

-   -   function calls: <function-name>([<argument-list>]);        <argument-list> is a possibly empty, comma-separated list of        expressions. There must be a function somewhere in the script        which takes parameters that match the return types of these        expressions in the order in which they occur. In the case of        functions that take references, the corresponding expression in        the <argument-list> of the function call must resolve to a        variable (not a constant or arithmetic/logical/relational        expression of multiple variables). The type of a function call        expression is the return type of its corresponding function        declaration.    -   string constants: “sample string \x3f”; these are string values        enclosed in quotes which mostly represent the literal characters        that comprise the string. The exceptions to this are the escape        characters: “\t” is tab, “\n” is newline, “\r” is carriage        return, and “\x[0-9a-fA-F][0-9a-fA-F]*” are embedded hex codes        that resolve down to one character. Note the regular expression        simply means for example “\x3F-sample” will resolve down to a 47        (0x3F) followed by a followed by a ‘s,’ etc. Any embedded zeros        (“\x0”) will terminate the string when the constant is used in        string expressions, but when used in binary expressions, the        total string will get processed to resolve the escape sequences        and then converted to type binary. String constants typically        have the same precedence as functions.    -   char constants: For example, ‘A’. These are treated the same as        string constants, except they are single quotes and single        character (which may be represented with escape sequences).    -   int constants: These can be decimal digits as in “1048576” or a        hexadecimal number as in “0x100F.”

Unitary Operators

-   -   ++<variable>: increment value of variable and then return its        value. Works on int and char.    -   −−<variable>: decrement value of variable and then return its        value. Works on int and char.    -   <variable>++: return value of variable then increment it. Works        on int and char.    -   <variable>−: return value of variable then decrement it. Works        on int and char.    -   −<expression>: negate whatever is returned by <expression> and        return that value. Works on int and char.    -   ˜<expression>: flip bits of whatever is returned by <expression>        and return that value. Works on int and char.    -   !<expression>: logical negation of <expression>. Works on        boolean.    -   sizeof(<typename> or <variable>): returns int that is how many        stack cells is occupied by the <typename> or <variable>.

Member Select Operator

-   -   <structurevariable>.<member>[.<member> . . . ]: returns whatever        type/value the rightmost <member> is.

Power Operator

-   -   <expression> power <expression>: lvalue and rvalue must be int        or char. If int and char mixed, promote char to int.

Multiply Operators

-   -   <expression>*<expression>: multiply . . . lvalue and rvalue must        be int or char. If int and char are mixed, promote char to int.    -   <expression>/<expression>: divide . . . lvalue and rvalue must        be int or char. If int and char are mixed, promote char to int.    -   <expression>%<expression>: modulo . . . lvalue and rvalue must        be int or char. If int and char are mixed, promote char to int.

Addition Operators

-   -   <expression>+<expression>: add . . . same type rules as multiply        operators but also does concatenation of two strings (returns        string) or two binaries (returns binary). If one of the        expressions is a string constant and the other is a binary        variable, the string constant will be considered a binary        constant.    -   <expression>−<expression>: subtract . . . same type rules as        multiply operators but also works on strings (not binaries as        operator+does). In the case of strings, subtraction removes all        substrings from lvalue that match rvalue and returns the        resulting string.

Bitwise Operators

-   -   <exnression><<<expression>: shift left one bit (effectively        multiply by 2). Same type rules as multiply operators.    -   <expression>>><expression>: shift right one bit (effectively        divide by 2 losing remainders). Same type rules as multiply        operators. Most significant bit (sign bit) is repeated in next        bit over.    -   <expression>&<expression>: bitwise and. Same type rules as        multiply operators.    -   <expression>|<expression>: bitwise or. Same type rules as        multiply operators.    -   <expression>̂<expression>: bitwise exclusive or. Same type rules        as multiply operators.

Relational Operators

All of these operators typically return boolean regardless of the typeson which they operate (in contrast to most operators which return thesame type as that on which they operate). Unless otherwise noted, lvalueand rvalue can be int/char and int/char or string and string. If theyare strings then the comparison is alphabetic case sensitive.

-   -   <expression><<expression>: Return true if lvalue is less than        rvalue.    -   <expression><=<expression>: Return true if lvalue is less than        or equal to rvalue.    -   <expression>><expression>: Return true if lvalue is greater than        rvalue.    -   <expression>>=<expression>: Return true if lvalue is greater        than or equal to rvalue.    -   <expression>=<expression>: Return true if lvalue equals rvalue.    -   <expression>!=<expression>: Return true if lvalue does not equal        rvalue.    -   <expression>in<expression>: This only works on string and binary        expressions. Return true if lvalue occurs as a        substring/subbinary pattern in rvalue.

Logical Operators

These operators expect lvalue and rvalue to return boolean and theoperators return boolean.

-   -   <expression>∥<expression>: “or else” . . . if lvalue is true        then return true without evaluating rvalue, else return whatever        rvalue returns.    -   <expression>&&<expression>: “and then” . . . if lvalue is false        then return false without evaluating rvalue, else return        whatever rvalue returns.

Assignment Operators

These operators insist on type compatibility which means equality oftypes most of the time. Exceptions are: when mixing ints and chars,lvalue type prevails, and when assigning string constants into binaryvariables the string constant becomes a binary constant. Lvalue andrvalue must resolve to scalar types and lvalue must resolve to avariable.

-   -   <expression>=<expression>: Simple assignment: copy rvalue into        lvalue.    -   <expression>*=<expression>:    -   <expression>/=<expression>:    -   <expression>%=<expression>:    -   <expression>+=<expression>:    -   <expression>−=<expression>:    -   <expression>>>=<expression>:    -   <expression><<=<expression>:    -   <expression>&=<expression>:    -   <expression>|=<expression>:    -   <expression>̂=<expression>: All the above perform the operator        preceding the “=” on the rvalue according to the rules of that        operator specified above and then put the result in the Ivalue.

Conditional Expression

There is also a construct identical in principle and syntax to theconditional expression in C/C++. Its syntax is:

(<expression>)?<expression-eval-if-true>: <expression-eval-if-false>;

If the expression in parentheses evaluates to true then the expressionafter the question mark is executed otherwise the expression after thecolon is executed. The expression in parentheses must resolve to booleanand the other two expressions must be type compatible. The returntype/value of a conditional expression is the return type/value of theexpression that executes after evaluating the conditional expression.

F. Control Structures

While Loops

A while loop is expresses as:

while (<expression>) { <statement-list> }or,

while (<expression>) <statement>;

This evaluates <expression> which must return boolean and executes the<statement-list> or <statement> and then reevaluates <expression> for aslong as <expression> returns true. If <expression> returns false thefirst time then the <statement-list> or <statement> is never executed.

Repeat Loops

repeat (<expression>) { <statement-list> }or,

repeat (<expression>) <statement>;

This evaluates <expression> once (in contrast to most loop constructswhich execute their “iterator” expression each time before executing theblock), and it must return an int or char indicating how many times toexecute the block. The block is then executed that many times. In casethe implications of this are not clear, note that in a while loop, forexample, the body of the loop must do something that eventually causesthe <expression> to evaluate to false, otherwise the loop goes onforever. But if the repeat loop's block does something that would causethe <expression> to evaluate differently, this makes no difference asthe <expression> is only evaluated once before the block is executed. So“v=2; repeat (v) {v=5;}” will not cause an infinite loop. Rather, itwill assign 5 to v twice.

If Statements

if (<expression>) { <statement-list> }or,

if (<expression>) { <statement-list> } else { <statement-list> }

For the sake of brevity, all possible options of using a single<statement> instead of {<statement-list>} have not been enumerated, butthose options exist. If <expression>, which must resolve to booleantype, evaluates to true then the first block is executed. If itevaluates to false and the else block exists, it is executed, otherwiseno block is executed.

For Loops

for (<expression-list>; <expression-list>; <expression-list>) {<statement-list> }or,

for (<expression-list>; <expression-list>; <expression-list>)<statement>;

The <expression-list> can be nothing, it can be a single <expression>,or it can be a comma-separated list of expressions. The first<expression-list> gets called initially and can be any mix ofexpressions as the return values are ignored. The middle<expression-list> is the condition that determines whether the blockwill be executed and whether the loop will continue to be iterated. Allexpressions in this list must return boolean and they all must returntrue in order for the block to be executed. The last <expression-list>can be any mix of expressions and it gets executed after each time theblock has been executed.

The classic example is “for (x=0; x<8; x++) {<statement-list>}” Thiswill set x to 0, test whether x is less than 8, find that to be true andexecute the block, increment x to 1, test whether x is less than 8, findthat to be true and execute the block . . . etc. until x is 8 which willcause the condition to be false and loop execution terminates.

G. Native Objects

The grammatical/syntactic elements of one embodiment of the FASLlanguage have been specified above. Notice that these things aresufficient to perform calculations and implement algorithms, but thereis nothing about them that allows for things like sending and receivingdata over the network and there are certain operations on the scalartypes that would be nice to have but are not expressible with thegrammar thus far specified. For this reason there exist structures andfunctions declared in the scope that owns the script scope (a“meta-scope” if you will) that allow access to this functionality. Asused herein “Faultline” refers to the overall network security system.

FASL Object

Every script has access to a variable named “FASL” whose type is“FASL_OBJECT.” This variable's type is specified as follows:

-------------- structure FASL_OBJECT { private: string m_szName,m_szDescription, m_szSummary, m_szReturnString; RETURNVALUEm_eReturnCode; int m_nDefaultPort, m_nIPAddress; ATTACK m_eAttackType;OPERATINGSYSTEM m_eOSMajor, m_eOSMinor; PROTOCOL m_eDefaultProtocol;public: function FASL_OBJECT( ) { m_nDefaultPort = 0; m_nIPAddress = 0;m_szReturnString = “Return string not set.” } function voidsetScriptName(string s) { m_szName = s; } function voidsetScriptVulnerabilityCode (int nFaultlineID) { // This sets thevulnerability id as it exists in the Faultline database that uniquely //identifies the vulnerability being sought by the script. m_nFaultlineID= nFaultlineID; } function void setScriptDesc(string s) {m_szDescription = s; } function void setScriptSummary(string s) {m_szSummary = s; } function void setScriptAttackType(ATTACK e) {m_eAttackType = e; } function void setScriptReturn(stringszReturnString, RETURNVALUE eReturnCode) { m_szReturnString =szReturnString; m_eReturnCode = eReturnCode; } function voidaddValidPort(int n) { // When a script successfully compiles, it willexecute all these that it finds // in the main scope. It builds a listof ports on which to run the script. m_nValidPort = n; } function voidsetScriptPort(int n) { m_nDefaultPort = n; } function voidsetScriptOS(OPERATINGSYSTEM eMajor, OPERATINGSYSTEM eMinor) { // When ascript successfully compiles, it will execute all these that it finds //in the main scope. It will use this information to decide whether thisscript // needs to be run on a given host. m_eOSMajor = eMajor;m_eOSMinor = eMinor; } function void setScriptProtocol(PROTOCOL e) {m_eDefaultProtocol = e; } function int getIPAddress( ) { returnm_nIPAddress; } function int getScriptPort( ) { return m_nDefaultPort; }function string strTok(string& s, string szDelimiters) { // Like strtokin UNIX, this skips past any characters at the beginning of the string// that are in szDelimiters. Return the substring that includes all theleftmost // characters up to but not including the next instance of acharacter in // szDelimiters, or the end of the string whichever comesfirst. Remove the // returned string from s (note it is a reference).return STRTOK(s, szDelimiters); } }; -------------

When a script is successfully compiled, all statements of the form“FASL.memberfunction( )” that are in the main scope are executed (and noother statements in the script are executed at this point). Theinformation that these member functions set goes into the scriptobject's data which allows the system to make some intelligent decisionson when and how to run the script. FASL.addValidPort(nPort) can becalled any number of times and will result in a list of unique portsbeing built up. When the system is run, it will either find thatFASL.addValidPort(nPort) was not called in the script's main scope inwhich case the script will be run once per host and FASL.getScriptPort() will return 0 within that script. If FASL.addValidPort(nPort) doesoccur in the main scope of the script, the system will execute thescript once for each unique port on a given host, andFASL.getScriptPort( ) will return whatever port the system passes in forthat execution. FASL.setScriptOS( ) operates along a similar principle(i.e., by calling it you are requesting that the script be executed onlyon hosts whose OS has been specifically determined whereas not callingit implies that the script is to be called regardless of OS). Note thatcalling this multiple times does not make a list of OSes like theaddValidPort makes a list of ports. The last call to setScriptOS is theone that gets used.

Upon entry into the script's scope, the m_nIPAddress member of the FASLvariable has been set to the IP address of the target machine upon whichthe FASL script is to run. All network activity that takes place in aFASL script uses this IP address as its destination, hence in thefunctions and objects about to be specified, the IP address is never aparameter. Calling FASL.setScriptReturn(string, RETURNVALUE) sets them_szReturnString member which is then printed by the script executorcommand line application “fasl.exe” upon completion of executing thescript. The other calls, most notably setScriptOS( ), set info that isused by Faultline.exe to determine whether or not to run the script on agiven host. This is to say, the system will execute only the “FASL.xxx()” statements in the script, then the system examines the memberdata anddecides whether or not to run the whole script on that IP address. Inone embodiment, the constructor of FASL_OBJECT is actually not called onthe FASL variable. Thus, any variable other than m_nIPAddress issometimes not be initially set to anything. Structures may be derivedfrom FASL_OBJECT and variables of type FASL_OBJECT may be initialized,in which case that constructor will be called. Note also that the membervariables of FASL are not directly accessible by script code (declaredas private).

Socket Object

This is a structure declared in the meta-scope but there are noinstances declared in the meta-scope as there is with FASL_OBJECT. It ismostly like a normal FASL structure, but the constructor creates awindows TCP or UDP socket depending on what you pass in for the firstargument of the constructor and the destructor cleans up that object.The member functions permits data to be sent or received on that socket,assuming it connected properly. The structure is as follows (the datamembers are omitted as it is not necessary to know them):

-------------- structure Socket { function Socket(PROTOCOL eProtocol,int nPort) { // eProtocol is either TCP or UDP and the port is the IPport. // Creates a windows socket object. } function ~Socket( ) { //Cleans up the Windows socket object associated with this socket. }function boolean socketOpen( ) { // Typically must be called beforesending or receiving data for either protocol. // if returns false thenit could not open the socket and communication // will fail. } functionboolean socketClose( ) { // Close the socket. destructor will do this ifnot done here. } function void BindPort(int nPort) { // Use when youwant specify the source port explicitly. BIND_PORT(nPort); } functionstring socketRead(int nBytes, int nTimeout) { // Read nBytes fromSocket... returns empty string if fail. } function stringsocketReadLine(int nBytes, int nTimeout) { // Read nBytes or up to endof line whichever comes first. // return empty string on fail. }function binary socketReadBinary(int nBytes, int nTimeout) { // ReadnBytes of raw binary data. empty binary on fail. } function intsocketWrite(string szBuffer, int nLength) { // Write nLength charactersout of szBuffer. return 0 on fail // or number of bytes written onsuccess. } function int socketWrite(string szBuffer) { // Write theentire string (length implicit), otherwise same as above. } function intsocketWrite(binary bBuffer) { // Write the binary raw data... lengthimplicit, otherwise same as above. } }; -------------

Vulnerability Object for Active Assessment

This object is used for active assessment, and its custombehavior—atypical of general FASL script—is that it knows how to copyitself, and all the data it needs to find itself later, into a globaldata area where other scripts can access the data, and use theinformation to attempt to compromise another machine. The object is asfollows:

-------------- structure Vulnerability { private: int m_nFaultlineID,m_nIPAddress, m_nExploitIPAddress; string m_szDescription; public:function Vulnerability( ) { m_nFaultlineID = 0; m_nIPAddress =0xFFFFFFFF; m_szDescription = \“Vulnerability uninitialized.\”; }function void addToExploitableData( int nFaultlineID, int nIPAddress,int nExploitIPAddress, string szDescription) { // This sets all themember variables of this structure. This function may be // called froma derived structure and this function will know that. It stores the //entire contents of the object as well as the object's typename and sizein the // global vulnerability data area. } function booleangetExploitableData(int nIndex) { // this function searches the globalvulnerability // data area for the nIndex-the instance of a variable ofthe same type as this (this // could be and probably will be a derivedstructure from Vulnerability) and copies // its contents into thisobject. If there is no nIndex-th object, return false and // no changeto this object's data will have occurred. } // Accessor functions. themembers of this structure need to be read only once they // have beenstored with addToExploitableData( ). function int getFaultlineID( ) {return m_nFaultlineID; } function int getIPAddress( ) { returnm_nIPAddress; } function int getExploitIPAddress( ) { returnm_nExploitIPAddress; } function string getDescription( ) { returnm_szDescription; } }; ---------------

Behind this object is the concept that one script may discover somethingthat another script can use to compromise another machine. Anyvulnerability needs the information contained in this base class, inthis embodiment. The m_nFaultlineID is the vulnerability id of thevulnerability discovered. The m_nIPAddress is the machine it wasdiscovered on. The m_nExploitIPAddress is the machine on which the datawas discovered that proved instrumental in finding this vulnerability.The m_szDescription is what you want to appear in the Active-Assessmentreport. The m_nExploitIPAddress should typically be set to −1 when noother vulnerability was used to find this vulnerability. When anothervulnerability is used, its m_nIPAddress (typically usingothervuln.getIPAddress( )) is entered into this vulnerability'sm_nExploitIPAddress. This will establish an audit trail which the reportcan represent graphically.

The general, usage of this is to derive a structure from Vulnerability,(i.e., “structure UnicodeVulnerability {// extra info specific tounicode vuln that can be used by other scripts};”). When a unicodevulnerability is found, for one example, a variable such as“UnicodeVulnerability uv;” is created, and its extra data is set andadded via a call to “uv.AddToExploitableData( . . . ).” After this call,another script that looks to make use of this particular vulnerabilityhas code resembling the following:

---------- int i; UnicodeVulnerability uv; for (i = 0;uv.getExploitableData(i); i++) { // Attempt to use this data tocompromise this host. if (succeed at compromising this host) { // createa vulnerability representing this host's vulnerability that was // foundusing the UnicodeVulnerability. Note that this vulnerability // may ormay not be a UnicodeVulnerability... it could be some other //vulnerability. When you have populated it with its specific data, call:newvuln.addToExploitableData( nNewVulnFaultlineID, FASL.getIPAddress( ),uv.getIPAddress( ), “we got this vuln by exploiting Unicode on anothermachine”); } } -----------

Debug Messages

There is a function called “debugMessage(<scalar>e)” overloaded for allthe scalar types. Mostly it prints what is expected from a debuggingsystem. Int and char print as numbers, boolean prints as “true” or“false”, strings print their contents. Binary produces a hex dumpoutput, through debugMessage(binary b), which closely resembles what theMS-DOS DEBUG.EXE “d” option produces. That is, it outputs out linesrepresenting 16 bytes each and the line format is “<4 digit hex offset>:<8 2-digit hex numbers separated by space>−<the other 8> <16 chars whereprintable chars are represented as is and non-printable are representedas periods>. For example:

-   -   “0060:67 65 6C 73 20 6C 6F 6F-6B 20 6C 69 6B 65 20 74 gels look        like t”

With the functions about to be specified, it is easy to convert othertypes into strings so you can debugMessage entire expressions . . . i.e.debugMessage(“here is what x equals:”+intToString(hex));. There istypically no need to remove or comment out debugMessage calls in scriptsthat get “signed off,” as final as the system execution of scripts willtypically ignore the debug output.

String functions ------------ function string leftTrim(string s) { //Lops off whitespace up to the first non-whitespace character. } functionstring rightTrim(string s) { // Lops off all trailing whitespace. }function int stringLength(string s) { // self-explanatory. } functionstring toLower(string s) { // Makes any characters that are upper-caselower-case. } function string toUpper(string s) { // Makes anycharacters that are lower-case upper-case. } function intstringToInt(string s) { // similar to atoi in C. } function stringintToString(int n) { // i.e 1048576 becomes string “1048576” } functionstring intToString(char c) { // Similar to intToString(int). } functionstring intToHexString(int n) { // i.e. 16383 becomes “3FFF” } functionint hexStringToInt(string s) { // i.e. “3FFF-blahblahblah” becomes16383. } function string intToBinaryString(int n) { // i.e. 85 becomes“1010101” } function int binaryStringToInt(string s) { // i.e.“1010101blahblahblah” becomes 85. } function string intToIPString(int n){ i.e. 16777215 becomes “0.255.255.255” } function string grep(strings1, string s2) { return \“to be implemented\”; } function intlocate(string s1, string s2) { // return 0-based position of s1 in s2 or−1 if s1 not in s2. } function string subString(string s, int nStart,int nNumChars) { // i.e. subString(“one law for the lion and ox isoppression”, 4, 3) = “law” // it is smart about boundries... if you askfor more characters than exist // you only get the ones that exist. }function string garbageString(char c, int nLength) { // i.e.garbageString(‘A’, 7) = “AAAAAAA” } function string garbageString(intnLength) { // return string of nLength length whose characters arerandom // upper and lower case alphanumerics. } ---------- Binaryfunctions: ---------------- function int binaryLength(binary b) { //self-explanatory. } function char binaryNthByte(binary b, int n) { //return nth byte numbered from 0. If out of bounds, // return −1. }function boolean binaryChangeByte(binary& b, int n, char c) { // Changebyte #n in binary b to c. If out of bounds, // do nothing to b andreturn false. } function binary binaryRight(binary b, int n) { // returna binary which is the rightmost n bytes of b. If there // are not nbytes in b, you get all of b (not padded to n). } function binarybinaryLeft(binary b, int n) { // same like binaryRight except from left.} function binary binaryMid(binary b, int nStart, int nLength) { //nStart is 0-based... return binary which is the nLength bytes starting// at nStart. If there are not nLength bytes, return however many thereare. } ---------- General global functions: -------------- functionstring getLocalHostIP( ) { // return string “xxx.xxx.xxx.xxx”representing the IP of the machine // on which the FASL script isrunning. } function string getTargetHostIP( ) { // This is in here forcompatibility reasons... you can get the same // effect by doing:intToIPString(FASL.getIPAddress( )); } function int getTargetPort( ) {return FASL.m_nDefaultPort; } function boolean RPCCheck(int nRPCProgNum){ // Attempt to make an RPC call on the given nRPCProgNum to see if itexists // on the target machine. Return true if it does. }function boolean SMBCheck(string szUserName, string szPassWord, stringszShare) { // Attempt to do a “net use” sort of thing on the givenshare... i.e. “IPC$”, // “\\HOSTNAME\C$”, “\\xxx.xxx.xxx.xxx\C$”, etc.If it succeeds then // promptly delete the share and return true,otherwise return false. } --------------

This implementation of the FASL scripting language permits one toperform active assessment of potential vulnerabilities on a known targetcomputer with known open ports. For example, a FASL script to test aunicode vulnerability has the form:

----------- structure UnicodeVulnerability extends Vulnerability {string m_szUnicodeString; }; function faslmain( ) { UnicodeVulnerabilityuv; uv.m_szUnicodeString = “The unicode string”;uv.addToExploitableData(1, FASL.m_nIPAddress, “the string for reportingpurposes”); debugMessage(“vulnfind executed.”); } structureUnicodeVulnerability extends Vulnerability { string m_szUnicodeString;}; function faslmain( ) { UnicodeVulnerability uv; if(uv.getExploitableData(0)) { debugMessage(“getExploitableData( )...m_nFaultlineID = ” + intToString(uv.m_nFaultlineID) + “, m_nIPAddress =” + intToIPString(uv.m_nIPAddress) + “, m_szDescription = ” +uv.m_szDescription + “, m_szUnicodeString = ” + uv.m_szUnicodeString); }else { debugMessage(“getExploitableData( ) failed.”); } }-----------------

Notably, information collected from a successful vulnerability test, inone embodiment, is used to advantageously further test the vulnerabilityof the target network and individual target computers. In particular, inthe event of a successful vulnerability test, additional ports or levelsof account access are typically available on the target computer. Thus,even if other prior vulnerability tests failed, they are advantageouslyretried after a successful vulnerability test.

FIG. 8 illustrates one embodiment of active assessment of avulnerability of a target computer on a target network. For simplicity,the network is shown as having a target 1 computer 800 and a target 2computer 802. For simplicity, a single vulnerability is assumed to applyto all TCP and UDP ports of the two computers. A single vulnerability‘TEST’ is tested on various TCP and UDP ports on both target computers.Prior host discovery and port discovery have provided target 1 data 804and target 2 data 806 that includes an identification of open portsfound on each target computer. Specifically, in the example illustratedin FIG. 8, TCP port 80 and UDP ports 5000 and 53 were found open on thetarget 1 computer 800, and TCP ports 23 and 80 and UDP ports 500, 53,and 1721 were found open on the target 2 computer 802. The activeassessment process starts in a step 806 and begins by executing a TESTroutine 808 that applies the TEST vulnerability to each port on thetarget 1 computer 800. In the example of FIG. 8, in a first round 810 oftesting the target 1 computer 800, the testing of ports 80, 5000 and 53result in no successful applications of the vulnerability. The systemthen moves in to a first round 812 of testing the target 2 computer,where testing of ports 80 and 53 are unsuccessful, but testing of ports23, 5000 and 1721 are successful. Upon successful testing, an attempt ismade to strip useful information from the target computer, and anyinformation retrieved is stored in the target 2 data 806. Based on thenew information retrieved, a second round 814 of testing the target 1computer is attempted. In this attempt, testing of port 80 is stillunsuccessful, but testing of ports 5000 and 53 is now successful withthe inclusion of the additional information gathered from the target 2data 806. In this manner, a second round 816 of testing the target 2computer is attempted. The rounds of testing are repeated untilvulnerability assessments can be actively completed for the entiretarget network.

Known vulnerabilities are typically stored in a database for inclusionin vulnerability assessment testing, active assessment and reporting. Inone embodiment, the “Vulns” table called “static data,” which onlychanges when deploying new patches incorporating new vulnerabilities.This would happen, for example, as new vulnerabilities are discoveredand existing in-the-field system installations need to be made aware ofthem. The present system uses, in one example, the VulnsFound tablebelow to indicate which vulnerabilities it has found on a particularscan. VulnsFound is simply an index into the Vulns table which keeps usfrom otherwise repeating the same data a multitude of times and wastingspace.

----- TABLE: Vulns COLUMN: BID, TYPE: varchar(10) COLUMN: CVE, TYPE:varchar(20) //“Common Vulnerabilities and Exposures” number. COLUMN:CyberID, TYPE: int(10) COLUMN: Description, TYPE: text(2147483647)COLUMN: ExploitDataType, TYPE: varchar(64) //Name of the FASL type,where applicable, that contains extra data for this vulnerability.COLUMN: ExploitDate, TYPE: smalldatetime(16) COLUMN: ExploitLink, TYPE:varchar(255) //Site where you can download the exploit/patch. COLUMN:FaultlineID, TYPE: int(10) //Primary key field... linked to VulnsFoundtable. COLUMN: Impact, TYPE: tinyint(3) COLUMN: ISSID, TYPE: int(10)COLUMN: LHF, TYPE: bit(1) //short term intrusion opportunity... true orfalse. COLUMN: Name, TYPE: varchar(128) COLUMN: NID, TYPE: int(10)COLUMN: Observation, TYPE: text(2147483647) COLUMN: Person, TYPE:varchar(50) COLUMN: Popularity, TYPE: tinyint(3) COLUMN: Recommendation,TYPE: text(2147483647) COLUMN: Risk, TYPE: tinyint(3) COLUMN: RiskText,TYPE: text(2147483647) COLUMN: Simplicity, TYPE: tinyint(3) COLUMN:Type, TYPE: varchar(50) //web, router, unix, trojan, etc. TABLE:VulnsFound COLUMN: ConfigurationID, TYPE: int(10) COLUMN: CustomerID,TYPE: int(10) COLUMN: FaultlineID, TYPE: int(10) COLUMN: HostID, TYPE:int(10) COLUMN: JobID, TYPE: int(10) COLUMN: VulnFoundID, TYPE: intidentity(10) -------

VII. Quantitative Scoring of Target Network Vulnerability

Network vulnerabilities have traditionally been rated on a “low risk,”“medium risk,” and “high risk” scale. This subjective scale is based onthe level of access to a target system granted by a vulnerability, theease of detecting and exploiting the vulnerability, the public knowledgeof a vulnerability, the percentage of computers subject to thevulnerability, and the like. However, this subjective scale lacksobjective indicia allowing comparison of otherwise heterogeneousnetworks for the purpose of comparing relative security. Further, thissubjective three-level scale provides little information about securityimprovement or added risks over time.

In one embodiment, the present system provides objective, quantitativeindicia of the overall security of the target network. Advantageously,this quantitative indicia can be any quantitative scale of sufficientgranularity to provide meaningful distinctions due to changes in networkvulnerabilities over time, with a range of between 1-10, 1-100, and thelike. Further, this objective indicia applies a standard formula to thevarious vulnerabilities discovered on the target network and networkconfiguration, such that a valid comparison can be made between thesecurity of otherwise heterogeneous network configurations, operatingsystems, and computers.

For example, the objective indicia is a risk measurement algorithm, suchas a FoundScore F. In one embodiment illustrated by the flowchart inFIG. 9, the FoundScore F is defined as:

F=100−V−E  (Eq. 1)

where,

-   -   F=FoundScore    -   V=Vulnerability Loss    -   E=Exposure Loss.

More specifically, in one preferred embodiment, the vulnerability loss Vis defined as the sum of values assigned to each vulnerability found onthe target network. For each of the n vulnerabilities found on thetarget network, that vulnerability is assigned a weight.

Thus, for a particular vulnerability V_(x), where 1≦x≦n, thevulnerability weight V_(w,x) is defined as:

$\begin{matrix}{V_{w,x} = \left\{ \begin{matrix}\left\{ 50 \middle| {{{PEA}\left( V_{x} \right)} \geq 2} \right\} \\\left\{ 10 \middle| {2 > {{PEA}\left( V_{x} \right)} \geq 1} \right\} \\\left\{ 5 \middle| {1 > {{PEA}\left( V_{x} \right)}} \right\}\end{matrix} \right.} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

where:

PEA(V_(x))=floor({P(V_(x))+E(V_(x))+A(V_(x))}/3)  (Eq. 3)

and:

-   -   floor(x) is the standard floor function,    -   P(V_(x)) is the popularity of the vulnerability on a 1-3 scale,    -   E(V_(x)) is the ease of exploitation of the vulnerability on a        1-3 scale,    -   A(V_(x)) is the level of access/privileges granted by the        vulnerability on a 1-3 scale,    -   where the higher the score on the scale the greater the risk.

Alternatively, the vulnerability can be simply defined as the risk levelassociated with the vulnerability, such as where:

PEA(V_(x))=R(V_(x))  (Eq. 3a)

where,

-   -   R(V_(x)) is the risk associated with the vulnerability on a 1-3        scale.

Typically, the factors used to determine the PEA(V) for a particularvulnerability are provided from the vulnerability database discussedpreviously. In other embodiments, the vulnerability base function (e.g.,PEA(V)) can be defined from a number of different variables, including,for example, ease of distribution of a vulnerability, ease of preventingthe vulnerability, and the like. Thus; the total vulnerability score Vis, in one embodiment, equal to:

V=min(50,Σ_((x=1→D)){V_(w,x)})  (Eq. 4)

where:

-   -   n=number of vulnerabilities found on the target network,    -   Σ=the summation symbol,    -   V_(w,x)=the vulnerability weight defined above, and,    -   min (x,y)=the standard minimum function.

The total exposure score E is, in one embodiment, defined as:

E=min(50,Σ_((y=1→q)){10×U_(y)+5×I_(y)+N_(y)+2×M_(y)})  (Eq. 5)

where:

-   -   q=the number of live target computers found on the target        network,    -   U_(y)=the open UDP ports found on the yth target computer,        except DNS,    -   I_(y)=the open ICMP ports found on the yth target computer,    -   N_(y)=the non-essential services found on the yth target        computer,    -   M_(y)=a penalty for target computers with no essential services,    -   Σ=the summation symbol, and,    -   min (x,y) is the standard minimum function.

In particular, the number of live target computers q is typicallydeduced from the host discovery process described above. The number ofopen UDP ports U_(y) found on the yth target computer is typicallydeduced from the service discovery and active assessment processdescribed above. The number of non-essential services N_(y) found on theyth target computer is typically deduced from the service discovery ofTCP and UDP ports, and in one preferred embodiment, counts all openports found on each target computer, except for certain predeterminedservices. Table 11 lists examples of predetermined services that are notincluded in the count of nonessential services N_(y) in accordance withone embodiment of the present invention.

TABLE 11 Example Essential Services not Included in N_(y) countEssential Service Ports HTTP 80, 8000, 8080 SSL/HTTPS 443 FTP 21 DNS 53SMTP 25

Other combinations of essential services are also possible, based onchanges in operating system, protocols, and the like. Finally, the noessential services penalty flag M_(y) is set to 1 for each targetcomputer that has N_(y)>0, and has no essential services running such asthose shown in Table 7. Otherwise, M_(y) is set to 0.

As a result, the FoundScore F=100−V−E provides a quantitative scorebetween 0 and 100 representing an objective indicia of the relativesecurity of the target network. Generally, the higher the Foundscore(i.e., the higher F is), the greater the relative security of the targetnetwork. Other embodiments are possible, such as, for example, where:

E_(alt)=[Σ_((y=1→q)){(5×U_(y)+2×I_(y)+2×N_(y)+2×M_(y))²}^(1/2) /q  (Eq.7)

V_(alt)=[Σ_((x=1→n)){(V_(w,x))²}]^(1/2) /n  (Eq. 8)

F_(alt)=E_(alt)+V_(alt)  (Eq. 9)

In this alternative scoring regiment, the higher the F_(alt) score theworse the target network security.

FIG. 9 illustrates one embodiment of a methodology for determining thesecurity score for a target network. In a first decision step 900, themethod determines whether all vulnerabilities found in the targetnetwork have been counted. If not, the method calculates PEA(V_(x)) (Eq.3) above, or a variation thereof, in a step 902 for vulnerability numberx based on predetermined values stored in a vulnerability database 904.The value of PEA(V_(x)) is used to calculate the weighted vulnerabilityV_(w,x) (Eq. 2) for a vulnerability x in a step 906. Typically, thevulnerability counter is then incremented in a step 908 if necessary fora particular embodiment. Thereafter, the method returns to the decisionstep 900 and again determines if all the vulnerabilities have beencounted.

After all the vulnerabilities have been counted, then in preferredembodiments, the total vulnerability V is calculated in a step 910. Asdiscussed above, the total vulnerability V is the lesser of either 50 orthe sum of all weighted vulnerability scores V_(w,x) in this embodiment.Alternatively, other scores are possible, or the tabulation of the totalscore V can be combined with the prior loop.

Then, in a decision step 912, the method determines whether all targetcomputers found in the target network have been counted. If not, theexposure values are determined in a step 914. In preferred embodiments,the exposure values include U_(y) (the open UDP ports found on the ythtarget computer, except DNS on port 53), I_(y) (the open ICMP portsfound on the yth target computer), and N_(y) (the non-essential servicesfound on the yth target computer), are determined. The exposure valuesare determined dynamically based on the network security test, and are,in one embodiment, stored in the target computer vulnerability database904 or in another database. In a step 916, a penalty M_(y) is determinedfor target computers with no essential services present. Preferably, theexposure counter is then incremented in a step 918, and the methodreturns to the decision step 912 to determine whether all the targetcomputers have been counted.

When all the target computers are counted, the total exposure E iscalculated in a step 920 as the lesser of either 50 or the sum of aweighted sum of the exposure values found. Then, in preferredembodiments, the score F is calculated in a step 992 as 100 minus thetotal vulnerability and exposure scores to generate a representation ofa network security score. In preferred embodiments, a greater value of Fimplies greater network security on an objective scale.

Other exemplary embodiments apply various permutations of the factorsassociated with vulnerability scoring and exposure scoring, and aresimilarly foreseen as within the disclosure herein.

VIII. Graphical Hierarchical Reporting of Target Network Topology andVulnerabilities

Generally, a conventional network security system provides reportinginformation in a text dump format. The collected data records regardingnetwork topology, target computers, vulnerabilities, and the like aredumped into an ASCII file that requires substantial effort to interpret.Such data dumps are used conventionally because, other than alerting thenetwork security user to the presence of high danger vulnerabilities,existing systems do not provide an interactive, hierarchical, andgraphical representation of the data representing the network, targetcomputers, and vulnerabilities found to assist the user in identifyingand correcting the specific vulnerabilities.

The present system compiles the data discovered during security testinginto a graphical, informationally hierarchical, and interactive set ofdocuments for review at various levels of detail and documentation.Thus, in one embodiment of the present invention, the reports engineproduces (1) a dynamic graphical display representing the networktopology, the target computers found, and the vulnerabilities foundthroughout the target network; (2) a comprehensive list of targetcomputers, vulnerabilities found, and vulnerability explanations; (3) anobjective scoring report describing the approximate security rating ofthe target network; (4) an exposure report describing the ports,services, and (5) detailed information that sets forth testing resultson a per-machine, per-port, or per-vulnerability basis. Certainindividuals within an organization may want different levels of detail.For example, upper management may only want the objective scoring report(3) that describes the approximate security rating of the targetnetwork. In contrast, the network administrator wants to receive allreports, particularly, the detailed information report (5) that enablesthe administrator to identify the machines and ports on the machinesthat need to be corrected.

For example, a functional representation of a report generated by thereport engine typically includes a quantitative score representationincluding (1) the actual score, (2) a color representation of the scoreexposure, and (3) a graphical representation of the quantitative score.The actual score is the F score or an alternative embodiment, such as,for example, a 1 to 100 numerical rating as described previously. Thecolor representation represents the overall vulnerability range of thescore. Thus, in one embodiment, a score between 1 and 33 will have a redcolor signifying high vulnerability, a score between 34 and 66 will havea yellow color signifying medium vulnerability, and a score above 66will have a green color signifying low vulnerability. Other colors,ranges, and representations, such as, for example, using icons orpictures to represent the vulnerability level, are foreseen.

FIG. 10, for example, illustrates an embodiment of a hierarchicalsecurity report 1000 presented on a display for viewing by a user. Thehierarchical security report includes a representation 1010 of theFoundstone score, showing a value of 15 corresponding to a relativelyhigh risk. The security report further includes a graphicalrepresentation 1020 of the mapped network topology, including the livetarget computers and the services located on the target computers. Thesecurity report further includes a list 1030 of discovered hosts, and alist 1040 of discovered services.

The user may select any of the reports shown in FIG. 10 (or otherreports that are not shown) and request additional details. FIG. 11, forexample, illustrates an embodiment of a hierarchical security report1100 that provides greater detail regarding the vulnerabilities of twotarget computers. For example, an upper portion of the displayidentifies a first target computer (“localhost.local.net” at IP address255.255.255.255) having a first open port represented by a window 1110and a second open port represented by a window 1120. Each of the openports of the first target computer has a respective vulnerability andmay identify a vulnerability patch to install on the target computer toreduce the vulnerability. As a further example, a lower portion of thesecurity report 1100 identifies a second target computer(“localhost2.local.net” at IP address 254.255.255.255) having a singleopen port represented by a window 1130. The information in the window1130 indicates that the service on the port is out of date, suggestingthat it should be removed, and advantageously identifies a vulnerabilitypatch to install if the service is to be retained.

There is an “object layer” implemented in C++ which represents thehierarchy of data objects that the system deals with, as described abovewith respect to the FASL scripting language. All objects follow themodel of 1) containing the data directly relevant to that object as datamembers (these are 1-1 correspondent with a row in the database) and 2)possibly containing lists of other objects that also follow thisconvention. Each object has a Load( ) and Save( ) member that deals withthe data for which that object is directly responsible by loading orsaving it from the database. For the “child” object lists, theUpdateToDatabase( ) and UpdateFromDatabase( ) member functions are used.These call the object's Save( ) or Load( ) members respectively. Theythen recursively call the child lists' UpdateToDatabase( ) orUpdateFromDatabase( ) members. In this way, objects and their childrencan be selectively loaded from any point in the hierarchy. This was donebecause the objects are generally too unwieldy to deal with all at once.

Once the data is loaded, an object which represents a single scan has aGenerateReport member function which programmatically generates all thehtml, gif, jpg, and png files that constitute the report. The html filesare generated by loading a “template” html file that containsboilerplate source and key words and replacing the key words with thehtml source representing the report data. The gifs and jpgs are simplybackground graphics that do not change from report to report so they arewritten as is without the report mechanism having to know the details ofgif and jpg encoding. For images that do need to be dynamicallycalculated, the png graphics format is used. This is a public(non-licensed) format for which there exists a public library which weare linking into the system executable. The images are drawn onto aWindows HDC (windows software object that represents a display device)and then converted into png by a custom class which wraps the object inthe proper format.

An exemplary Scan Summary Report is set forth below in Appendix A. Acorresponding exemplary FoundScore Report is set forth below in AppendixB. A corresponding Network Topology Report is set forth below inAppendix C.

Although the above description of the present invention includes atleast one embodiment of the system, it should be understood that variouschanges, substitutions and alterations can be made to the system withoutdeparting from the spirit and scope of the invention as defined by theclaims herein. For example, one alternative embodiment of themethodology described above is exemplified in FIG. 12.

1-11. (canceled)
 12. A method comprising: identifying a set of activecomputer devices on a network; assessing each computer device in the setagainst a first vulnerability in a plurality of known vulnerabilities,wherein each vulnerability in the plurality of known vulnerabilities hasa corresponding vulnerability script adapted to perform an automatedassessment of a computer device against the respective vulnerability,and assessing each computer device against the first vulnerabilityincludes executing a first vulnerability script; storing, in memory,results of the assessments of each computer device in the set againstthe first vulnerability as returned from the executed firstvulnerability script; and providing at least a portion of the resultsfor use by a second vulnerability script in an automated assessment ofat least a portion of the computer devices in the set against a secondvulnerability included in the plurality of known vulnerabilities. 13.The method of claim 12, wherein identifying the set of active computerdevices includes detecting the set of active computer devices asresponsive within a plurality of computer devices on the network. 14.The method of claim 13, wherein identifying the set of active computerdevices includes transmitting a set of ICMP packets, a set of TCPpackets, and a set of UDP packets to at least a portion of the pluralityof computer devices and monitoring responses to the sent packet sets.15. The method of claim 12, wherein each vulnerability script is aFASL-based script.
 16. The method of claim 12, wherein eachvulnerability script is adapted to copy itself to a global memorylocation for access by other vulnerability scripts.
 17. The method ofclaim 12, wherein each computer device in the set is assessed againstthe first vulnerability in parallel using the first vulnerabilityscript.
 18. The method of claim, 12, wherein the assessment resultsinclude identification of failure or success of the first vulnerabilityscript to exploit the first vulnerability.
 19. The method of claim 18,wherein exploiting the first vulnerability includes compromising atarget computer device using the first vulnerability script.
 20. Themethod of claim 12, wherein the first vulnerability script comprises aninstantiation of a vulnerability object class.
 21. The method of claim20, wherein the vulnerability object class includes an identifierattribute identifying a corresponding vulnerability, a machineidentifier attribute identifying at least one machine possessing thecorresponding vulnerability, an exploited machine identifier attributeidentifying machines on which data was discovered allowing the discoveryof the corresponding vulnerability, and a vulnerability descriptionattribute describing the corresponding vulnerability.
 22. The method ofclaim 12, wherein the assessment results are stored in a data recordassociated with the first vulnerability.
 23. The method of claim 22,wherein providing at least a portion of the results includes preparing adata record including the portion of the results and adapted to becalled by other vulnerability scripts including the second vulnerabilityscript.
 24. The method of claim 23, wherein the portion of the resultsincludes information collected from a previously-assessed computerdevice describing attributes of the previously-assessed computer deviceand the information is used by the second vulnerability script in theautomated assessment of the portion of the computer devices against thesecond vulnerability.
 25. The method of claim 24, wherein thepreviously-assessed computer device is included in the portion of thecomputer devices in the set.
 26. The method of claim 12, wherein theassessing each computer device in the set against a first vulnerabilityincludes assessing a first port of each computer device and theassessment results identify at least one other open port on at least oneof the assessed computer devices.
 27. The method of claim 26, whereinthe identification of the at least one other open port is included inthe portion of the results and used by the second vulnerability scriptin the automated assessment of the portion of the computer devices inthe set against the second vulnerability.
 28. Logic encoded innon-transitory media that includes code for execution and when executedby a processor is operable to perform operations comprising: identifyinga set of active computer devices on a network; assessing each computerdevice in the set against a first vulnerability in a plurality of knownvulnerabilities, wherein each vulnerability in the plurality of knownvulnerabilities has a corresponding vulnerability script adapted toperform an automated assessment of a computer device against therespective vulnerability, and assessing each computer device against thefirst vulnerability includes executing a first vulnerability script;storing, in memory, results of the assessments of each computer devicein the set against the first vulnerability as returned from the executedfirst vulnerability script; and providing at least a portion of theresults for use by a second vulnerability script in an automatedassessment of at least a portion of the computer devices in the setagainst a second vulnerability included in the plurality of knownvulnerabilities.
 29. A system comprising: at least one processor device;at least one memory element; and a network security engine, adapted whenexecuted by the at least one processor device to: identify a set ofactive computer devices on a network; assess each computer device in theset against a first vulnerability in a plurality of knownvulnerabilities, wherein each vulnerability in the plurality of knownvulnerabilities has a corresponding vulnerability script adapted toperform an automated assessment of a computer device against therespective vulnerability, and assessing each computer device against thefirst vulnerability includes executing a first vulnerability script;store, in memory, results of the assessments of each computer device inthe set against the first vulnerability as returned from the executedfirst vulnerability script; and provide at least a portion of theresults for use by a second vulnerability script in an automatedassessment of at least a portion of the computer devices in the setagainst a second vulnerability included in the plurality of knownvulnerabilities.
 30. The system of claim 29, further comprising a scanengine adapted to execute either of the first or second vulnerabilityscript in connection with a vulnerability scan of a particular computerdevice on the network.